Meter terminal unit for use in automatic remote meter reading and control system

ABSTRACT

A meter terminal unit for use in automatic meter reading systems of the type including a control center for transmitting commands to and receiving measurement data from the terminal unit via a distribution unit serving several terminal units. The terminal unit is selectively responsive to commands generated by the control center to carry out load control operations, encoder meter reading and store operations, or transfer previously stored meter data from the terminal unit to the control center in accordance with functions specified by the various commands.

This is a division of application Ser. No. 799,550, filed May 23, 1977,now U.S. Pat. No. 4,161,720.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to remote automatic meter reading andcontrol systems and more particularly to a meter terminal unit ortransponder for use in such systems to effect the carrying out of meterreading and load control operations at terminal points along acommunication line such as a utility power transmission network.

2. Description of the Prior Art

Utility companies have long used meter reading personnel for reading theconsumed commodity information provided by utility meters (i.c. gas,water, electricity, and the like). However, in recent years significantstrides have been made in the development of fully automatic meterreading systems.

Most remote meter reading systems have similarities in their designs.Generally, they comprise some type of encoder device attached to a meterto give an indication of the meter reading, means for storing the meterreading indicated and a transponder for transmitting meter data over acommunication link to a central station or control center wheninterrogated by a signal from the central station. One known systemutilizes a mobile van which travels over a specified route in acommunity and, while traveling, transmits interrogate signals to meterequipment transponders at the houses located along the traveled route.The transponder at each house, in response to the interrogating signals,transmits a message to the van which includes a meter identificationnumber and the present reading of the meter. Receiver equipment in thevan effects the storage of the meter data for subsequent use in billingthe customer.

Various other types of systems have been developed which utilize thetelephone lines of the subscriber as the communication link to thecentral station. Also, there are arrangements in which the power linesof the subscriber and the utility company are used as the link betweenthe customer's meter and the central station.

While many communication systems have been developed for utilitycompanies, all of which utilize one or more of the various links andequipment aforementioned, no known economical feasible meter terminalunit or transponder has yet been designed for use in such systems whichaffords the capabilities of mass meter data accumulation and loadcontrol at a consumer residence and which meets the universal needs ofutility companies.

An electric power network, involving as it does a vast number of meterlocations, logically dictates that the most economical communicationsystem will be that system which affords a minimum expenditure for thetransponder equipment at each meter location, while allowing a greaterexpenditure for more sophisticated equipment for the processing of largeamounts of meter data and the rapid distribution of command informationto the transponder meter locations. This logical consideration hasgenerally made the approach of providing radio receiver transmitterunits at each meter location unfeasible. In effect this approachinvolves the use of as many communication systems as there are meterterminal locations. The desired approach, by contrast, would utilize anexisting communication network which links all meter terminal locationstogether and would minimize the expense of the control equipment at eachterminal location. Further, overall system control would be effected bya control station and section or group equipment which being required insmaller numbers can be of greater sophistication.

Additionally, the desired system would allow utility companies to readall meters in a city at desired intervals, such as during daily peakpower periods. This has the advantage of allowing the utility companiesto improve the system load factor by encouraging the customer to improvehis residential load factor. This improvement of load factor can beaccomplished in a number of ways by effecting a shifting of loads on thesystem from on-peak periods to off-peak periods. Three modes, but notnecessarily all inclusive, of accomplishing this load-shift have beensuggested as follows:

1. Alerting the customer by the automatic activation of an indicator athis residence via a meter terminal unit when he is using energy duringpeak periods so that he can reduce his load during those periods.

2. Metering and billing the customer at a premium rate for his on-peakusage as determined from stored meter data collected from the customer'smeter terminal unit.

3. Controlling or limiting the customer's on-peak usage of energy byautomatically turning off various loads in his residence (e.g. hot waterheaters, clothes dryer, etc.) via a meter terminal unit during thoseperiods.

Thus, it can be seen that a need exists for an improved meter terminalunit for use in an automatic meter reading and control system whichaffords the preceding advantages and which has a built-in flexibility toaccomodate future changes in utility company operating philosophy.

The system disclosed herewin, which makes use of the present invention,is also disclosed and claimed in U.S. patent application, Ser. No.653,859 filed Jan. 30, 1976, now U.S. Pat. No. 4,135,181 entitled"Automatic Remote Meter Reading and Control System" and is assigned tothe same assignee as the present invention.

SUMMARY OF THE INVENTION

The aforementioned advantages are provided by the present invention bythe provision of a new and improved transponder or meter terminal unitfor use in a remote automatic utility meter reading and control systemwhich responds to commands from a control center to read and store meterdata representative of a measured commodity reading and to transfercommodity readings to the control center via communication lines such asa network of power lines. Additionally, the meter terminal unit respondsto commands from the control center to selectively energize orde-energize a plurality of loads connected to the terminal unit.Typically, these loads are indicator lights which are turned on atspecific times by the power company to notify the customer that he isusing power during on peak periods, or relays which can be activated andde-activated to control the power applied to various appliances such asrefrigerators, air conditioners, hot water heaters, dryers and the like.

The commands received by the terminal unit of the present invention areof various types with each type having at least an address portion and afunction code portion for identifying the terminal unit and directingits modes of operation respectively.

A meter terminal unit may have one, or a plurality of meters with eachmeter including an encoder capable of generating data signalsrepresentative of a commodity reading measured by the meter.

A command is received and stored by the terminal unit. The address andfunction code portions of the command are decoded to effect variousmodes of operation to be carried out by the meter terminal unit. Themeter terminal unit will re-act to a command only when the meterterminal unit recognizes its address as specified by the contents of theaddress portion of a command. The function code portion of the commanddirects the meter terminal unit to carry out its specified operations.

In response to a read and store meter data operation, the function codedirects the meter terminal unit to effect the reading of data signalsrepresentative of a commodity reading from any one of the various metersinto selected ones of a plurality of storage means in the meter terminalunit. In one read and store meter reading operation, a particular metercan be selected to cause that meter's encoder to transfer meter datainto any one of a plurality of storage means in the meter terminal unitfor subsequent transfer to the control center via the communicationlines.

In response to a different read and store meter data operation, any oneof several meters can be individually selected, as specified by thefunction code, to store their meter data into a single storage means inthe meter terminal unit for subsequent transfer to the control center.

Meter data previously stored in the various storage means in the meterterminal unit can be selectively transferred from those storage means inresponse to commands received and stored by the meter terminal unit.When the meter terminal unit recognizes its address and the functioncode contents specify that information is to be transmitted from themeter terminal unit to the control center, the function code will effectselection of one of the storage means in the meter terminal unit for thetransfer of that storage means data to the control center.

From the preceding discussion, it can be seen that the meter terminalunit of the present invention provides the capability of reading andstoring meter data from a plurality of meters, whereby the meter datacan be stored for an indefinite period of time until it is desired touse that data. When it is desired to use the stored meter data, thecontrol center merely commands the meter terminal unit to transmit itspreviously stored meter data from the selected storage means to thecontrol center for subsequent use by the utility company, such as forbilling the customer or meter survey purposes, etc.

Additionally, one or more consumer loads such as indicator lights orrelays may be controlled by the meter terminal unit in response to aspecified type of control command sent to the meter terminal unit fromthe control center. In this particular type of command, when the meterterminal unit recognizes its address, one or more of the several loadsis either energized or de-energized in accordance with the contents ofthe function code portion of the command. The controlling of loads ofthis type at a consumer residence may be of benefit to the customer aswell as to the utility company by allowing the utility company to turnon indicator lights to indicate to the customer that he is using powerduring a peak power period during which period his billing will behigher. If the customer sees an indicator light on at a specific timeand realizes the meaning of that indicator, he can thus plan to use lesspower during that period to conserve on his electric bill.

Additionally, by being able to control various relays in a customerresidence, the utility company can turn on and off air conditioningunits during specific periods of the day as well as control otherappliances such as hot water heaters and electric clothes dryers. Inthis manner, it is possible for the utility company to effectivelycontrol the various loads on their power system network to conserveenergy.

In the system contemplated, in which the invention finds its use,section control units may also be utilized to channel informationbetween the control center and the various meter terminal units whichare connected to the section control units. In this type of system,several meter terminal units communicate with one section control unit.In this type of system, it is desirable that the meter terminal unitrespond only to the commands received from its associated sectioncontrol unit. In this instance, all commands received by the meterterminal unit include a further address portion which identifies thesection control unit which is transferring commands to that meterterminal unit. When a command is received by a meter terminal unit, itrecognizes its own address as well as the address of its associatedsection control unit in order to perform the functions specified by thecommands.

The invention also contemplates apparatus or means for synchronizing aserial stream of data signals, such as from a serialized meter encoder,with a clock signal derived from a source of alternating current toprovide the data signals as synchronized by the clock signal.

In the exemplary embodiment, the encoder and a clock signal generatingmeans are responsive to the alternating current. The encoder providesdata signals to the clock signal generating means which includessynchronization means for synchronizing the clock signal with the datasignals.

Means are also provided for combining the clock signal with the datasignals.

Means are also provided for combining the clock signal and the datasignals to enable the provision of the data signals, as synchronized bythe clock signal, to a storage means, such as a register.

It is therefore an object of the present invention to provide a meterterminal unit or transponder for use in a remote automatic meter readingand control system having enhanced operating capabilities.

It is another object to provide a meter terminal unit for use in anautomatic utility meter reading system responsive to commands from acontrol center capable of selectively reading, storing and transferringa measured consumed commodity reading over a communication network tothe reading control center.

A still further object is to provide a meter terminal unit for use in acomputerized data communication system of the type capable of readingmeter data from a plurality of residence meter terminal units undercommand control of a computer.

It is another object to provide a meter terminal unit for use in anautomatic meter reading system which provides the selective capabilityof simultaneously reading and storing meter data from a plurality ofmeters and simultaneously transmitting the stored meter data to acomputer under command control of the computer.

It is a further object to provide a meter terminal unit for use in anautomatic meter reading and control system capable of receiving commandsfrom a control center over a communication line via a control unit toeffect the selective carrying out of meter read and store andinformation transfer operations as well as load control operations inresponse to commands received by the meter terminal unit.

Still another object is to provide apparatus for synchronizing a serialstream of data signals with a clock signal to provide the data signalsas synchronized by the clock signal.

Yet another object is to provide apparatus for synchronizing a serialstream of data signals with a clock signal and combining the data andclock signals to provide the data signals to a storage means assynchronized by the clock signal.

BRIEF DESCRIPTION OF THE DRAWING

The present invention may be more readily understood by reference to theaccompanying drawing in which:

FIG. 1 is a major block diagram of the system of the present invention.

FIGS. 2-6 illustrate the various formats of messages and datatransferred between units of the system.

FIGs. 7 and 8 are flow charts useful in understanding the sequence ofoperations which take place in the system.

FIGS. 9, 10, 11, 13, 14, 15, 19, 21 and 22 are legendary drawingsshowing the inter-relationships between FIGS. 9A and 9B, 10A-10D,11A-11H, 13A-13F, 14A-14D, 15A-15D, 19A-19D, 21A and 21B, and 22A-22D.

FIGS. 9A, 9B, 10A-10D, 11A-11H, and 12 are timing diagrams useful inunderstanding the operation of the section control units of FIG. 1.

FIGS. 13A-13F and 14A-14D are detailed block diagrams of a typical oneof the section control units of FIG. 1.

FIGS. 15A-15D, 17, 19A-19D and 22A-22D are detailed block diagrams of atypical one of the meter terminal units of FIG. 1, and

FIGS. 16, 18, 20, 21A and 21B and 23 are timing diagrams useful inunderstanding the operation of the meter terminal units of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT System Description

Reference is now made to FIG. 1 of the drawing, which presents a blockdiagram of the overall system. System control is directed by a readingcontrol center 10 (hereinafter referred to as the RCC), which iscomprised of a data processor or digital computer. The computer is of ageneral purpose type having sufficient memory capacity to store datapertaining to the entire system and is programmed to transmit messagesor commands throughout the system and to collect data from the system asdescribed herein below. Many such digital computers are commerciallyavailable. For a relatively small system, the PDP8/E computermanufactured by the Digital Equipment Corporation is suitable. For largesystem applications, the H4010 data processor manufactured by theHoneywell Corporation may be employed. It is to be noted that each ofthese computers contains its own input/output equipment for the transferof commands and the receipt of data between the RCC and the rest of thesystem.

The RCC 10 issues commands and receives data preferably in a multiplexmode over a plurality of digital input/output serial transmission lines12. It will be noted that some of the lines 12 are connected to modems(modulator/demodulator circuits), which in turn provide communicationwith a plurality of section control units 16 (SCU) over individual voicegrade or trunk lines 14 of the conventional dedicated telephone type.Each SCU 16 also has a conventional modem for interface between itstrunk line and the logic internal to the SCU. Transmission of databetween the modems is preferably of the frequency shift keying (FSK)type; however, other types of transmission may also be employed. Each ofthe modems are preferably of the voice frequency type comprised of acommercially available transmitter/receiver. Typical transmitters andreceivers of the type which may be employed in the present system aremodels 68T,2F and 68R,2F, respectively, manufactured by RFL Industries,Inc., Boonton, New Jersey. These transmitter/receivers are documented inthe RFL Industries, Inc. publication entitled Voice-Frequency CarrierEquipment, Series 6850, revised May 1975.

Certain other ones of the digital input/output lines 12 of the RCC areconnected directly to the SCU's 16. In most applications, the SCU's willbe located at such a distance from the RCC that it is desirable to usethe modem in order to properly amplify the signals transmitted overlines 12 and 14. However, there may be situations where one or moreSCU's are directly adjacent the RCC, in which case signal strength willbe large enough that it is unnecessary to employ the modem.

For purposes of simplicity, the system is illustrated with several SCU'sconnected to only one modem via their associated voice grade line 14. Itis to be understood that all of the other lines 14 could likewise haveSCU's connected thereto in the same fashion.

It will be noted that each of the SCU's is connected to an associatedelectrical power transmission line 18. Each of the power lines also hasconnected thereto at least one meter terminal unit 20 (MTU). In thepreferred embodiment, the transfer of commands and data between the RCCand the SCU's over the voice grade lines 14 is in ASCII code format.Commands or messages issued by the RCC are transferred from the SCU's totheir corresponding power lines as digital data consisting of pulses ofRF energy at a pulse repetition frequency of preferably 30 Hz. It willbe noted in FIG. 1 that output messages from the SCU's are designated asbeing transferred at a frequency of f_(o) as indicated by the arrowgoing downward on the page adjacent each power line 18. The designationf_(o) indicates the pulse frequency of each bit of transmitted data.Also, as shown in FIG. 1, each SCU, if desired, is capable oftransmitting messages at a different frequency as indicated by the f_(o)' and f_(o) " notations.

As will be more fully described, each SCU is uniquely addressable and isalso capable of recognizing an ALL SCU address in commands received fromthe RCC. Further, each SCU is capable of recognizing a function codecontained within the command to determine the action that it is to take.Message parity is also checked by each SCU. If an SCU recognizes itsaddress, and the command contains proper parity, the SCU will transferthe command onto its associated power line 18. Depending on the contentsof the function code, the SCU will go into one of two modes. If thefunction code specifies that no data is to be received over the powerline from one or more MTU's, the SCU will revert to a standby mode.However, if the function code specifies that data is to be received fromone or more MTU's, the SCU will go into a receive data mode and wait forreceipt of data from the MTU(s) for transfer to the RCC.

It is significant to note that when the reading control center (RCC)issues a command over a voice grade line 14, the SCU's connected to thatline simultaneously receive that command. Only those SCU's recognizingtheir assigned address(s), as specified by the command, will transferthat command over their corresponding power lines 18.

As previously mentioned, messages are transmitted at a frequency of f₀over each SCU's respective power line to a plurality of meter terminalunits (MTU's) connected to each of those power lines. In response tocertain commands, the MTU's will respond with data representative of ameasured commodity at a specified frequency.

Table 1 illustrates representative power line transmission or carrierfrequencies which may be employed in the system. A Set No. column in thetable specifies a set number of a group of frequencies in the rowcorresponding to the Set No. The frequency in the f₀ column specifiesthe power line carrier frequency of messages transmitted by the variousSCU's. The frequency in the f₁ -f₈ columns specifies the power linecarrier frequencies transmitted by a group of eight MTU's connected tothe power line by the SCU transmitting the f₀ carrier in the Set No.corresponding to those frequencies (f₁ -f₈).

It will be noted that the MTU's 20 on each power line 18 are organizedinto groups, such as Group 1 through Group N in FIG. 1. Likewise, Nnumber of groups comprise one set of N MTU groups. Each MTU in a grouptransmits its data at an assigned frequency. For example, in Group 1 itis shown that an MTU 20' transfers its data at a frequency f₁, whereasan MTU 20" transfers its data at a frequency f₈. All other MTU's, notshown in Group 1, transmit their data at corresponding frequencies f₂-f₇. Preferably, the data transferred from the MTU's to the SCU's is at30 bits per second with data pulse bursts of energy at frequencies f₁through f₈.

    __________________________________________________________________________    POWERLINE CARRIER FREQUENCIES                                                 Set                                                                              f.sub.0                                                                           f.sub.1                                                                           f.sub.2                                                                           f.sub.3                                                                           f.sub.4                                                                           f.sub.5                                                                           f.sub.                                                                            f.sub.7                                                                           f.sub.8                                    No.                                                                              Hz  Hz  Hz  Hz  Hz  Hz  Hz  Hz  Hz                                         __________________________________________________________________________    1  31410                                                                             30030                                                                             30450                                                                             30870                                                                             31290                                                                             31710                                                                             32130                                                                             32550                                                                             32970                                      2  34830                                                                             33390                                                                             33810                                                                             34230                                                                             34650                                                                             35070                                                                             35490                                                                             35910                                                                             36330                                      3  38370                                                                             36930                                                                             37350                                                                             37770                                                                             38190                                                                             38610                                                                             39030                                                                             39450                                                                             39870                                      4  41730                                                                             40290                                                                             40710                                                                             41130                                                                             41550                                                                             41970                                                                             42390                                                                             42810                                                                             43230                                      5  45210                                                                             43770                                                                             44190                                                                             44610                                                                             45030                                                                             45450                                                                             45870                                                                             46290                                                                             46710                                      6  49050                                                                             47610                                                                             48030                                                                             48450                                                                             48870                                                                             49290                                                                             49710                                                                             50130                                                                             50490                                      __________________________________________________________________________

Reference is now made to the meter terminal units 20 (MTU's) of FIG. 1.Each of the MTU's is located at metering locations such as householdresidences, business residences, factories or the like. The primarypurpose of each MTU is to provide communication interface between theSCU's 16 via the power lines 18 and commodity measuring meters 22 andelectrical loads 24 connected to the MTU's. Each MTU responds tomessages or commands to read and store meter data representative of ameasured commodity such as the consumption of power, water or gas, andtransmit the previously stored data to the RCC via the MTU's associatedSCU. Each MTU also responds to commands to control user loads within aresidence such as hot water heaters, air conditioners, alert lights,etc.

A command function code specifies to the MTU's whether meter informationis to be read and stored, whether the previously stored information isto be transmitted over the power lines or whether a load or loads is tobe controlled. The function code also specifies a particular meter to beread or a load(s) to be controlled.

The MTU's are individually addressable, group addressable or addressablein large sets comprised of several groups. A set may encompass all MTU'son a power line. One MTU is generally addressed when it is desirable tointerrogate only one residence, for example, during meter surveyoperations. During normal meter reading operations, however, groups ofeight MTU's are generally addressed. The purpose of this will becomemore clear in the ensuing description. There are situations in a largepower system of the type shown in FIG. 1 when it is either desirable, ornecessary, to quickly remove all loads from the entire system. Thiswould occur under conditions of a catastrophic power failure whichnecessitates a mass scramble to shutdown an entire system to preventdamage to the power transmission equipment. In this latter situation,the MTU's can be addressed in large sets or, if desired, all MTU's in anentire system can be simultaneously addressed. Set addressing of theMTU's can also be used for the mass reading and storing of the meterdata in the MTU's for subsequent transmission.

The unique addressing scheme of the system permits calling on smallconcentrated groups of MTU's for the transmission of meter data or forthe performance of various functions in large geographically dispersedsets of MTU's for simultaneous actions such as read and store data orload control.

There are many such meters on the market suitable for employment in thepresent system. In the preferred embodiment, however, the metersemployed have encoders for transferring consumed commodities such aspower, water or gas to the MTU's for storage for transmission at a latertime. Several types of encoder type meters are known such as contactswitch closure types, parallel switch contact types, optical read-out,etc. The present system preferably employs a mechanical non-destructivestorage encoder which provides a meter serial data readout as disclosedin U.S. Pat. No. 3,846,789, issued Nov. 5, 1974, entitled Remote-ReadingRegister with Error Detecting Capability, to Warren R. Germer et al andassigned to the assignee of the present invention.

Message and Data Formats

Prior to proceeding with a further description of the system, it isconsidered advantageous at this time to provide a detailed descriptionof the various message and data formats of the information transferredbetween the RCC and the SCU's and MTU's of the system. Reference is nowmade to FIG. 2, which illustrates the format of the messages or commandstransferred from the RCC to the SCU's. It will be noted that the messageis in ten bit ASCII code format wherein each character is comprised of astart bit at the beginning of the character and a stop bit at the end ofthe character. Eight bits of information are included between the startand stop bits of each character. The first character received by an SCUfrom the RCC is an SCU address. The second character forms a portion ofthe MTU address. It will be noted that the third character is comprisedof three bits of MTU address and five bits of information which specifyan SCU/MTU function code. The decode of these five bits by the SCUspecifies to that unit its mode of operation. If the function codespecifies that either a control or a meter read and store function is tobe performed by an MTU(s), then a data response is not expected by theSCU, and it will revert to the standby mode after transmission of themessage to the MTU(s). If, however, the function code specifies thatinformation is to be received from the MTU, the SCU will go into a waitor data receive mode. After the MTU(s) data has been received by the SCUand transferred to the RCC, the SCU will revert back to the standbystate in preparation for receipt of another message from the RCC.

The last character in the message received by the SCU from the RCC is aparity character. The present system employs the well-knownBose-Chauduri check code generated by the Polynomial 1+X+X⁶ operating onthe 24 message bits transmitted from the RCC to the SCU, and on 36 bitsof data transmitted by each MTU. Only six bits of the eight-bit paritycharacter are used, the last two bits being ignored. Even though the useof parity is described in the present system, it forms no part of theinvention and is merely illustrated for a more simple understanding ofthe disclosure. It is to be understood that other types of parityschemes could be just as effectively used.

Reference is now made to FIG. 3, which illustrates the message format ofmessages transferred from an SCU(s) to an MTU(s). It will be noted inthis message that the start and stop bits do not exist. Logic within theSCU removes or strips off the start/stop bits and appends to the frontof the message a start message code of three bits having the binaryconfiguration of 001. These start bits are used by the MTU to detect thestart of a message from the SCU. It will also be noted that the SCUpasses the message intact as received minus the start/stop bits. Thatis, it transfers the SCU address in an eight-bit field, the MTU addressin an eleven-bit field, the MTU function code in a five-bit field andthe six-bit parity code. For purposes to be later described, it shouldbe noted at this time that the SCU regenerates the SCU address and doesnot pass that address on precisely as received from the RCC.Additionally, the SCU regenerates parity because a portion of themessage address may be altered.

Reference is now made to FIG. 4, which shows the data format of messagestransmitted from an MTU(s) to an SCU(s). As previously mentioned, theMTU responds to basically three different commands: Read and store,perform a control action, and transmit a meter reading. As such, asshown in FIG. 4, the only data transferred from the MTU's to the SCU'sover the power lines is a message carrying information or datarepresentative of the meter dial readings from the encoder of anaddressed MTU meter. When an MTU receives a transmit command from theSCU, the message format as shown in FIG. 4 is transmitted by the MTU.The MTU, like the SCU, generates three message start or sync bits asbinary 001 for recognition by the SCU to detect the start of a messageor data word. Further, the meter encoder generates an identificationcode (ID), as the second six-bit character. The generation of this codeis shown and described in the aforementioned U.S. Pat. No. 3,846,789,and is for use by the RCC computer program to identify the particularmeter being read.

Following the meter encoder identification code are five six-bit binarycharacters generated by the meter encoder representative of meter dialreadings 1 through 5. The last character in the message transferred bythe MTU's to each SCU is the six-bit parity code. It is to be emphasizedthat the message format shown in FIG. 4 is representative of the datamessage transmitted by each addressed MTU to an SCU over the powerlines.

As previously mentioned, in the present system groups of MTU's (e.g.,eight MTU's) can be simultaneously addressed to transfer theircorresponding meter data to the SCU. In the present system, when a groupof eight MTU's is addressed, these eight MTU's basically transfer themeter data simultaneously over the power lines to their correspondingSCU. Also, as previously mentioned, this transmission of data from eachMTU is at a different frequency corresponding to each MTU. Each SCUcontains eight narrow-band receiver amplifier circuits capable ofdiscriminating between the frequencies of the messages from each of theeight MTU's. As a result, when eight separate messages are placed on thepower line, the SCU is capable of receiving each of those eight messagesin its corresponding amplifiers.

Reference is now made to FIG. 5, which shows the message or data formatof information from an addressed group of eight MTU's and how thatinformation appears on the power lines at the SCU's. Not shown in FIG. 5are the three message start or sync bits 001 generated by each MTU. Itwill be noted that when eight MTU's are simultaneously addressed totransmit information to an SCU, the message bits of each MTU aretransmitted simultaneously in a serial fashion onto the power line. Thefirst character to be transferred by each MTU (at their correspondingfrequencies f₁ -f₈) is the first identification code bit of theaddressed encoder or meter of each one of the MTU's 1-8 (See FIG. 1).Not shown in FIG. 5, but also transmitted immediately thereafter are the2nd, 3rd, 4th and 5th identification code bit characters. Next, thesixth identification code bits are transmitted from the MTU's 1-8.Following the last character containing the meter identification codebits are the meter dial readings (dials 1 through 5) in correspondingbits characters 7th through 36th. Following the 36th bits character arebits characters 37th through 42nd, which contain the parity bitsgenerated by each of the MTU's. The information as shown in the messageformat of FIG. 5 is received a bit at a time in each of the eightseparate channel receivers of the SCU and assembled in the SCU intoeight-bit ASCII characters for transfer to the RCC for processing.

Reference is now made to FIG. 6. Comparing the message formats of FIGS.5 and 6, it can be seen that a great deal of similarity exists betweenthose formats. The SCU, in reformating the message for transfer to theRCC, first appends a start and stop bit to each character developing theASCII code. As previously described, each MTU message to the SCU iscomprised of 42 bits (i.e., minus the three message start bits). The SCUdetects these three message start bits; however, they are removed beforethe message is transferred to the RCC. As can be seen in FIG. 6, themessage is transferred basically intact as shown in FIG. 4. That is, thefirst character transferred from the SCU to the RCC is comprised ofeight bits corresponding to frequencies f₁ -f₈ from each of the MTU's 1through 8. Each of these bits corresponds to one bit from the MTUgenerating the message bit at that specific frequency. The messageformat of FIG. 6 is basically the same format of FIG. 5, wherein bits1-8 of characters 1-6 of the message comprise the meter encoderidentification code for eight MTU's. Bits 1-8 of characters 7-36comprise the meter dial readings of meters 1-5 of each of the eightMTU's and bits 1-8 of characters 37-42 comprise the parity bits for eachof the eight MTU's.

Although not forming a part of the present invention, it is worth notingthat the RCC program receives the data in the format shown in FIG. 6 andorganizes that data by assembling each of the bits of the charactersinto complete words corresponding to data from each of the MTU's. Oncethis data is formatted into words corresponding to each of the MTU's,then that data can be appropriately processed by a computer program forbilling purposes, load control, meter surveying, etc.

System Operation-Flow Charts

FIGS. 7 and 8 are flow charts showing the sequence of operations for theentire system. Referring first to FIG. 7, there is shown a flow chartwhich exemplifies the operation of the system during the generation of aread and store or load control sequence by the RCC. The initiation of acommand from the RCC is indicated by a start circle in FIG. 7. The readand store or load control command is provided to one of the voice gradetrunk-lines 14 (FIG. 1) activated at that time by the RCC. The messageis then received by the SCU's on that line, which check to see ifmessage parity is okay and if the address contained within the messageis meant for one or all of the SCU's. If an SCU does not recognize theaddress, or if the parity check is bad, that SCU branches through a noexit into an "SCU resets to standby" block. That SCU will thus remain ina standby mode pending receipt of another message. If, however, an SCUdetermines that the parity check is okay, and that the address containedwithin the message is meant for that SCU, it exits through a yes branchinto an action block wherein the SCU proceeds to retransmit the commandonto the power line and reset to standby.

The message now being transferred onto the power line goes to each ofthe MTU's connected to that power line. Each MTU checks to see if theparity of the message is okay. Each MTU also checks to see if themessage address is meant for that MTU and if the function code is valid.If any one of these conditions does not properly check, the MTU willexit a no branch, at which time it resets to a standby mode inpreparation to receive another message. However, if all of the tests arevalid, the MTU exits through a ves branch and the function code isdecoded to determine which operation is to take place by the MTU. If thefunction code is detected as a read and store command, the program exitsthrough an R & S branch into an action block wherein the MTU reads thespecified meter encoder of one of a plurality of meter encoders andstores the meter dial readings of that encoder into a designated one ofseveral registers in the MTU as specified by the function code. The MTUthen resets to the standby mode. It is in this manner that the MTU canbe commanded to read and store meter information for subsequent recallby the program in response to an MTU transmit command to subsequently bedescribed.

Referring now back to the "which function code?" decision block, if thefunction code is decoded as a load and store command, the MTU then exitsthrough an LC branch. The LC branch enters into an action block whereinthe MTU or MTU's, if more than one is addressed, actuates the specifiedload or loads to perform a designated operation or operations asspecified by the function code. Upon termination of the load controloperation(s), the MTU then resets to standby in preparation to receiveanother message.

Reference is now made to FIG. 8, which is a flow chart showing how eachMTU responds to a transmit command issued by the RCC. Similarly to FIG.7, the RCC, in a start circle, initiates the transmission of a transmitcommand to a selected one of the trunk lines 14 to the SCU(s) on thatline. The SCU(s) connected to that trunk line checks the message parityand address as described for FIG. 7. If either of these conditions fail,a no branch is taken out of the "SCU Parity Address OK?" decision blockand the SCU resets to standby. If, however, the parity and addresschecks are positive, the SCU exits through a yes branch into an actionblock wherein the SCU retransmits the command onto the power line andthen goes into a wait mode for receipt of the meter data from theaddressed MTU(s). The MTU(s) then checks the parity, address andfunction code as previously described. If either of these checks fail,the MTU exits through a no branch and resets to standby. If allconditions are positive, however, the MTU(s) begins to transmit themeter data from the register as specified by the function code in thetransmit command. After the MTU(s) has transmitted all of the meter datafrom the designated register, it resets to the standby state inpreparation to receive another command.

SECTION CONTROL UNIT (SCU) OPERATIONAL DESCRIPTION

Reference is now made to FIGS. 9, 10, 11, 13 and 14, which are legendarydrawings showing the inter-relationships between the various drawings ofthe SCU.

The timing diagrams showing the operation of the SCU are shown in FIGS.9A and 9B, FIGS. 10A-10D, FIGS. 11A-11H, and the detailed logic of theSCU is shown in FIGS. 13A-13F and 14A-14D. The various shift registers,counters, flip-flops and gating circuits utilized in the construction ofthe SCU are preferably fabricated from integrated circuit logic.

The various blocks comprising the above-mentioned circuits may befabricated from commercially available devices as listed in Table 2. Thelisting in Table 2 gives the manufacturers' names, the manufacturers'part number and the circuit name identification as shown in the drawing.Footnotes 1-5 at the end of Table 2 give the manufacturers' referenceswhere the various circuits can be found.

                                      TABLE 2                                     __________________________________________________________________________    SECTION CONTROL UNIT                                                          MANUFACTURERS' CIRCUIT                                                        IDENTIFICATION                                                                                                  MANUFACTURER'S                              CIRCUIT NAME      MANUFACTURER    NO.                                         __________________________________________________________________________    MODEM             RFL INDUSTRIES,.sup.1                                                                         TRANSMITTER                                                   INC.            (68AT-WF-D)                                                                   RECEIVER                                                                      (68R-2F-5)                                  DATA TRANSMITTER/ GENERAL INSTRUMENT.sup.2                                                                      AY-5-10131                                  RECEIVER          CORP.           AY-5-10134                                  REVEIVER DATA MEMORY                                                                            SIGNETICS CORP..sup.3                                                                         S54170                                      REGISTER                                                                      CHARACTER COUNTER "               S5493                                       WRITE CHARACTER F/F                                                                             "               S5474                                       SYSTEM CONTROL F/F                                                                              "               S5474                                       PARALLEL IN SERIAL                                                                              "               S54166                                      OUT REGISTER                                                                  RESPONSE EXPECTED F/F                                                                           "               S5474                                       FFEF              "               S5474                                       FFDF              "               S5474                                       RTSFF             "               S5474                                       PLRFF             "               S5474                                       SAXFF             "               S5474                                       GRFF              "               S5474                                       POWER LINE CONTROL                                                                              "               S54161                                      COUNTER                                                                       REGISTER READ OUT/                                                                              "               S54161                                      ADDRESS CHECK COUNTER                                                         S/R CONTROL F/F   "               S5474                                       SCUADD F/F        "               S5474                                       POWER LINE XUITR F/F                                                                            "               S5474                                       ISEC DELAY FOR NEXT                                                                             "               S5490                                       CHAR.                                                                         30 Ms DELAY COUNTER                                                                             "               S5495                                       3 Ms DELAY CONTROL F/F                                                                          "               S5474                                       STATE F/F         "               S5474                                       STORE A F/F       "               S5474                                       STORE B F/F       "               S5474                                       267 Ms DELAY ÷ COUNTER                                                                      "               S5492                                       FF1A              "               S5474                                       50 Ms F/F         "               S5474                                       FF2A              "               S5474                                       EOM F/F           "               S5474                                       50 Ms DELAY ÷ 12 COUNTER                                                                    "               S5493                                       30 Hz STROBE CLOCK                                                                              "               S5493                                       COUNTER                                                                       MESSAGE LENGTH COUNTER                                                                          "               S54161                                      φA, φB, φC, φD F/F's                                                            "               S5474                                       REMOVE START BITS "TWO S5473                                                  COUNTER                                                                       ONE SHOT          "               S54121                                      NARROW BAND       TEXAS INSTRUMENTS.sup.4                                                                       THREE                                       RECEIVER/AMPS     INC.            SN52709AL                                   BAND PASS FILTER  GENERAL INSTRUMENTS.sup.5                                                                     TWO AY-6-4016                                                 CORPORATION     INTERCONNECTED                                                                THROUGH AN                                                                    SN52709AL                                   __________________________________________________________________________     .sup.1 This modem can be found in RFL Industries, Inc. Boonton, N.J.          U.S.A., publication entitled, VoiceFrequency Carrier Equipment, Series        6850, revised 5/75.                                                           .sup.2 This circuit can be found in General Instruments Corp.                 Microelectronics Technical Bulletin entitled, UAR/T Universal Asynchronou     Receiver/Transmitter, AY5-1013/AY-5-1013A, March 1974.                        .sup.3 All Signetics circuits, including logic gates not listed in Table      1, can be found in the manual entitled, Signetics Digital Linear MOS Data     Book, copyright 1974.                                                         .sup.4 This circuit can be found in the Texas Instruments, Inc. manual        entitled, The Linear and Interface Circuits Data Book for Design              Engineers, copyright 1973.                                                    .sup.5 This circuit can be found in General Instruments Corp. Advance         Bulletin 1970, entitled MTNS 16 Channel Random/Sequential Access              Multiplexer AY6-4016.                                                    

The operation of the SCU will be described in basically two modes ofoperation. The first mode will be with the SCU starting in standby andits operation when receiving a message from the RCC and the transmissionof that message onto the power line for receipt by an MTU(s). The secondmode of operation to be described will be with the SCU in the wait modeand its operation when receiving meter data over the power line from anMTU(s) and the transfer of that data to the RCC.

Let it first be assumed that power has just been applied to the SCU.With the application of power, a power on reset block 26 in FIG. 13Aapplies a binary 1 reset pulse to an R terminal of a system controlflip-flop 28 via an OR gate 30 and a conductor 32. Flip-flop 28 nowresets generating a binary 1 SCU reset signal on a conductor 34connected to an 0 output terminal of flip-flop 28. The SCU reset signalis applied to the various registers, counters and flip-flops in the SCU,causing those devices to all reset to a binary 0 state and placing theSCU in the standby mode.

Referring now to FIG. 13E, there is shown a master clock generator 36now generating a plurality of output timing signals for use incontrolling the SCU timing operations. These various timing signals areshown connected to the appropriate circuits in the SCU as well as beingshown in the aforementioned SCU timing diagrams.

Reference is now made to FIGS. 9A and 13A. In FIG. 9A at the top of thetiming diagram, there is shown a message from the RCC appearing at areceiver/demodulator 38 of an SCU modem on a trunk line 14. Aspreviously described, this message is transmitted in ASCII code usingFSK transmission techniques. Transmission is preferably at 300 baud. Thereceiver 38 passes the message in serial form into a data transmitterreceiver circuit 40 via a conductor 42. The data transmitter receiver 40is a universal asynchronous receiver/transmitter LSI subsystem whichaccepts binary characters from either a terminal device such as a modem,or a computer such as the RCC. As will subsequently be described, thissubsystem also receives data characters in parallel. Data output fromthis subsystem is also in serial or parallel.

As previously described in connection with FIG. 2 and as shown in FIG.9A, all incoming characters to the SCU from the RCC contain a start bit,eight data bits and a stop bit. As shown in FIG. 9A, when the datatransmitter/receiver 40 detects a mark to space transition, it detectsthat transition as the start bit of a character and begins to take inthe eight data bits plus the stop bit. When the tenth bit (end of thefirst character) is received by the data transmitter/receiver 40, thatcircuit generates a binary 1 data available signal DAV on a conductor44. The DAV signal is applied simultaneously to a set input(s) of awrite character flip-flop 46, as one input to an AND gate 48 and to aone-second delay circuit 50 of FIG. 13C via a conductor 49.

The presence of the DAV signal at AND gate 48 causes that gate to beenabled due to three binary 1 output signals, CCA, CCB, CCC, applied togate 48 from a character counter 52 via a plurality of conductors 54.With AND gate 48 enabled, a binary 1 CCO (character count 0) signal isgenerated on a conductor 56 and applied to a set(s) input terminal ofthe system control flip-flop 28, setting the latter.

It will be recalled, at the outset of the present discussion, flip-flop28 was reset when power was applied to the system. With the systemcontrol flip-flop 28 now set at the time shown in FIG. 9A, the SCU resetsignal goes to a binary 0 removing the reset signal from all counters,registers and flip-flops in the system, thus freeing the system to run.

Reference is now made back to the write character flip-flop 46, which isset by the DAV signal. As can be seen in FIGS. 9A and 13A, the writecharacter flip-flop generates a write enable signal WE on a conductor58, which is applied as an enable signal to a receive data memoryregister 60 to effect the parallel transfer of the eight-bit datacharacter now in the data transmitter/receiver 40 into the receive datamemory register via conductors 62.

The receive data memory register 60 is basically an LSI memory capableof storing a complete 32-bit message (four eight-bit characters) intoselectable character locations of that memory. The locations in the datamemory register are selected by a plurality of address signals CCA andCCB (called write select in FIG. 13A) on conductors 64 from thecharacter counter 52. As shown in FIG. 9A, the WE signal allows thefirst message character to be loaded into the receive data memoryregister into a location specified by CCA and CCB. It will be noted thatthe write character flip-flop 46 receives at its reset (R) inputterminal a 48 kHz clock signal from the master clock generator 36 ofFIG. 13E. This signal is shown in FIG. 9A resetting flip-flop 46.

As soon as the write character flip-flop 46 is reset by the 48 kHzclock, its one-output terminal causes the WE signal to go to a binary 0and its 0 output terminal to go to a binary 1 generating a Reset DAVsignal. As shown in FIG. 13A, this latter signal is applied to the datatransmitter/receiver 40 and to the character counter 52 via conductors66 and 68, respectively. The Reset DAV signal causes the DAV signal tonow go to a binary 0 and simultaneously causes the character counter 52to count up to a count of one as shown in FIG. 9A (CCA set). With thecharacter counter now setting at a count of one, it can be seen that theCCA signal is at a binary 1 and the CCB signal is at a binary 0, thusapplying the proper input address signals to the receive data memoryregister 60 on conductors 64 for receiving the second message character.

The second, third and fourth characters will continue to be taken intothe data transmitter/receiver 40 and placed in the proper characterpositions of the receive data memory register 60 under control of theCCA, CCB and WE signals in the manner just described. As shown in FIG.9A, when the fourth character has been loaded into the receive datamemory register, the CCC output of the character counter 52 goes to abinary 1, indicating that the receive data memory register is full.

A momentary digression is now made in the present description byreferring to FIG. 13A to the one-second delay for next character circuit50. It will be noted that that circuit receives the DAV signal and a 48kHz clock signal. The purpose of the one-second delay is to cause theSCU to reset if it does not receive a data character within one secondfrom the generation of the first DAV signal. If a character is notreceived within the one-second time interval, a binary 1 time-out signalon conductor 70 is applied to the system control flip-flop via OR gate30 causing the SCU to reset. In this manner, should a false start bitcome down the telephone line 14 from the RCC, the system will not befalsely triggered into operation. It will also be noted that the CCCsignal from the character counter is applied to an inhibit input of theone-second delay via conductor 72. The CCC signal is normally a binary 0to enable the one-second delay through a circle inverter. However, whenthe CCC signal goes to a binary 1, that signal is inverted to a binary 0inhibiting the operation of the one-second delay and preventing thetime-out signal from being generated after the last character has beenfully loaded into the receive data memory register.

Reference is now made to a register read-out/address check counter 74 ofFIG. 13C receiving the CCC signal from the character counter 52. The CCCsignal is a binary 0 until the character counter has counted to itsmaximum (count of 4). When the CCC signal is a binary 0, it provides aninhibit/reset input signal to an R terminal of counter 74 preventing thecounter from counting and keeping it in the binary 0 or reset state. Asshown in FIGS. 9A and 9B, when the CCC signal goes to a binary 1, theinhibit/reset signal is removed, enabling the register 74 to begincounting at a 48 kHz rate as shown by a start RR and ACC line in FIG.9B. FIG. 9B is actually a continuation of FIG. 9A, but it is based on adifferent time frame with all timing derived at a basic 48 kHz rate.

The purpose of the register read-out/address check counter 74 is togenerate coded count output signals to control the operational timing ofthe SCU during checking of the message received from the RCC.

It will be noted that register 74 generates six output signalsdesignated RCA through RCF on a plurality of conductors 76. The finalstage of register 74, designated RCF, is applied as one input to an ANDgate 78 as RCF. The other input to AND gate 78 is the 48 kHz clocksignal as shown in FIG. 13C. Since register 74 is reset at this time,the RCF signal is a binary 1, thus enabling AND gate 78 to allow the 48kHz clock to be applied as a register count signal RCNT to a trigger (T)input terminal of register 74. The relationships between the RCA throughRCF signals are shown in FIG. 9B. Since register 74 is astraight-forward binary counter, only signals RCA, RCB and RCF areshown, it being understood that the operation of such type counters iswell understood by those of ordinary skill in the art.

A decode network comprised of two sets of AND gates 80 and 82 in FIG.13C receives the RCA-RCF output signals from register 74 to generate theproper control signals for controlling the operation of the SCU.Reference is first made to an AND gate 84 of the group of AND gates 80receiving input signals RCA, RCB and RCC. As shown in the timing diagramof FIG. 9B, a binary 1 read enable 1 signal is generated on conductor 86from AND gate 84 in response to the just described input logicconditions. The read enable 1 signal is applied via conductors 86, 88and an OR gate 90 as a read enable signal to the receive data memoryregister 60. The read enable signal is also applied as a shift/loadsignal to a parallel in-serial out-register 92 via a conductor 94 toenable that register to receive a parallel character from memoryregister 60.

The read enable signal now enables the receive data memory register 60to transfer the first message character, in parallel, via its outputdata lines 96 through a conventional multiplexer circuit 98 into theparallel in-serial out-register 92. Addressing of the receive datamemory register is controlled by two input signals RSA and RSB onconductors 100 from two OR gates 102 and 104. The OR gates 102 and 104receive respective input signals RSA1 and RSB1 via conductors 106 and108 from the output of register 74. These two signals are actually theRCD and RCE outputs of register 74. As can be seen in the timing diagramof FIG. 9B, during the transfer of the first character from memoryregister 60 into registry 92, the RCD (RSA1) and RCE (RSB1) signals arebinary 0's. These two binary 0 signals effect the generation of binary0, RSA and RSB signals to cause the read-out of the least significantcharacter of the message from the receive data memory register. byreferring to FIG. 2, it can be seen that this first character is the SCUaddress character.

The SCU address character, which is now present in the parallelin-serial out-register 92, is the first character to be checked. Thischaracter is checked as follows: Reference is now made back to FIG. 13Cto the group of AND gates 82, wherein one of those AND gates 110 isreceiving the read enable signal and an output signal on conductor 112from another AND gate 114, the latter receiving the 48 Khz clock and thetwo input signals RCD and RCE from the register read-out address counter74. Since these latter two signals are now binary 1's, AND gate 114 isenabled to allow the 48 kHz clock to be applied to AND gate 110generating a check address (first character) output signal on aconductor 116. The generation of this latter signal is shown in FIG. 9Bin coincidence with the read enable signal applied to the memoryregister 60 and register 92.

The check address (first character) signal on conductor 116 is appliedto two gate logic structures labeled, this SCU address compare gates 118and all SCU address compare gates 120 of FIG. 13E. As previouslymentioned, each SCU is capable of recognizing its own distinct addressas well as an address which is common to all SCU's in the entire system.The comparison of the address in these two gate structures is effectedby the parallel input address bits being applied thereto from thereceive data memory register via a data bus 122.

The comparison of the distinct SCU address in gate structure 118 iseffected by a comparison of the SCU address now applied from the receivedata memory register with a plurality of binary signals TSCUA (this SCUaddress) on conductors 124 from a box 126 designated this SCU fixedaddress. Box 126 may be hardwired or switch selectable to apply theappropriate binary input signals (TSCUA) to the compare gate structure118. The contents of box 126 is preferably switch settable so that eachSCU can easily be assigned its own address. If the address from thereceive data memory register does not match the TSCUA addressingsignals, a fail 1 signal is generated on conductor 128 and applied viaan OR gate 130 of FIG. 13D to the set(s) input terminal of an SCUaddress flip-flop 132.

The ALL SCU address compare gate structure 120 contains its ownhardwired address for comparison with that address coming from thereceive data memory register. The logic in box 120 is designed torecognize an address common to all SCU's in the system. If the ALL SCUaddress compare does not check with the message address, compare gates120 will also generate a fail 2 signal on conductor 134. This latterfail signal is also applied to the SCU address flip-flop 132 via OR gate130.

Setting of the SCU address flip-flop 132 generates a binary 1 outputsignal designated address compare fail on a conductor 136, which isapplied to the system control flip-flop 28 via OR gate 30 to reset theSCU. Thus, it can be seen, upon examination of the very first characterof a message, if the address does not match the ALL SCU address or theaddress of the specific SCU, the system will revert immediately to thereset or standby mode. The timing for setting and resetting the SCUaddress flip-flop 132 is shown in FIG. 9B.

Let it now be assumed that the address check is valid. Under thiscondition, as can be seen in FIG. 9B, the read enable 1 signal is againgenerated (the second read enable 1 signal) to again enable the receivedata memory register to gate the data in parallel through multiplexer 98into the parallel in-serial out-register 92. The second data characteris the MTU address (see FIG. 2), which is gated from the secondcharacter position of the receive data memory register under control ofthe RSA and RSB signals as previously described. At this time the RCDsignal is a binary 1 and the RCE signal is binary 0. Thus, the RSA1signal is in binary 1 and the RSB1 signal is a binary 0. It is thedecode of these two signal states which selects the second characterposition out of the receive data memory register 60. This data characteris loaded into the parallel in-serial out-register. However, as shown inFIG. 9B, the MTU address is not checked.

After the MTU address is loaded into the parallel in-serialout-register, the next character to be read into that register from thereceive data memory register is the third message character, the SCU/MTUfunction code (see FIG. 2). As shown in FIG. 9B, the third read enable 1signal is now applied to the receive data memory register in conjunctionwith the RSA and RSB signals on conductor 100. At this time the RSA1signal is a binary 0 and the RSB1 signal is a binary 1 (RCD is a binary0 and RCE is a binary 1). Thus, the third data character is selected outof the receive data memory register and transferred via the multiplexer98 into the parallel in-serial out-register. At this time, the functioncode is to be checked to see if the message from the RCC is of that typewhich dictates a response from an MTU(s). This is accomplished by thegeneration of a check function (third character) signal on a conductor138 from an AND gate 140 of the group of AND gates 82 for application toan MTU response function compare gate structure 142 (see FIG. 13C).

Referring to AND gate 140 and to FIG. 9B, the check function signal isgenerated as a result of the decode of the binary 1 RCD and RCE signalsalong with the 48 kHz clock applied to AND gate 142, the output of whichis applied as one input to AND gate 140 along with the read enable 1signal on conductor 86. The generation of the check function signaleffects a comparison of a hardwired coding in the MTU response functioncompare gates 142 with the coding of the third character now applied inparallel to that gating structure from the receive data memory register60. If there is no comparison between the SCU/MTU function code and thewired function code, a normally binary 0 signal on a conductor 144applied to a set(s) input terminal of a response expected flip-flop 146remains at binary 0, thus leaving that flip-flop in the reset state.

With the response expected flip-flop 146 in the reset state, its one (1)output terminal is a binary 0 signal REFF on a conductor 148, which isapplied to an inverter 150. The output of the inverter 150 is a binary 1signal REFF, applied as one input to an AND gate 152. If no response isexpected, AND gate 152 will be enabled at a later time by a signaldesignated PL34 to apply a reset (no response expected) signal to thesystem control flip-flop via a conductor 154 and OR gate 30. Thegeneration of the PL34 signal will subsequently be described.

Let it now be assumed, however, that the function code of the commandspecifies that a response is expected from a meter terminal unit(s). Inthis case, the response expected signal on conductor 144 will go to abinary 1 causing the response expected flip-flop 146 to set. Flip-flop146 now generates a binary 1 REFF signal on conductor 148. The REFFsignal is applied via conductor 148 and 156 as one input to an AND gate158 of FIG. 13B. The other input signal to AND gate 158 is the PL34signal to subsequently be described. As can be seen (FIG. 13B), when thePL34 signal is generated, a power line received flip-flop PLRFF 160 willbe set generating a binary 1 output signal designated PLRF to turn onall of the SCU power line receivers. The operation of the PLRFFflip-flop will be described in more detail later.

It should also be noted at this time that the REFF binary 1 signal isalso applied via a conductor 161 to a transmitter modulator 162 of themodem to turn on the carrier signal for the transmission of a datamessage to subsequently be received from the addressed MTU or MTU's. Itshould also be noted that when the REFF signal is a binary 0, thetransmitter modulator carrier signal is turned off or diabled. Thiswould be the situation when the response expected flip-flop 146 isreset.

Reference is now made back to FIG. 9B. After the SCU/MTU function codehas been checked and the response expected flip-flop either set or leftin the reset state, the fourth read enable 1 signal is generated toeffect the transfer of the 4th character from the receive data memoryregister 60 into the parallel in-serial out-data-register 92. As can beseen in FIG. 2, this 4th character is the parity character. At this timethe selection of that 4th character from the receive data memoryregister is effected by the two binary 1 states of the RSA and RSBsignals (RCD and RCE, both binary 1's). It will be noted, however, thatparity is not checked concurrently with the presence of the read enable1 signal, as in the case of the first and third characters of themessage. A check parity (4th character) signal is applied via aconductor 164 to a parity check generate circuit 166 from the output ofan AND gate 168. The generation of the check parity signal is the resultof the ANDING in an AND gate 170 of the RCA, RCB, RCC and the ANDING inan AND gate 172 of the RCD, RCE and 48 kHz clock signals. The output ofAND gates 170 and 172 enable AND gate 168 to generate the check paritysignal on conductor 164. The operation of the SCU under a parity checkfail condition will be described later in more detail.

In order to further understand the operation of the SCU, it is nownecessary to refer to a shift register control flip-flop 174 as shown inFIG. 13C. Referring now to FIGS. 13C and 9B, it is shown that the shiftregister control flip-flop 174 is set via a conductor 175 from AND gate176 enabled by the binary 1 signals RCD, RCE and read enable 1.Flip-flop 174, now generating a binary 1 output signal on conductor 178from its 1 output terminal, enables an AND gate 180 also receiving the48 kHz clock signal. The output of AND gate 180 is a gated 48 kHz signaldesignated G48KHZ on a conductor 182. The G48KHZ signal is applied to anOR gate 184 of FIG. 13A. The output of OR gate 184 is applied as a clockdata signal on conductor 186 to a trigger (T) input of the parallelin-serial out-register 92. The purpose of the clock data signal is tocontrol the parallel loading and serialized shifting of the parallelin-serial out-register.

Reference is now made to FIGS. 9A, 9B and 13A. As previously described,the read enable signal on conductor 88 is also applied as a shift/loadsignal on conductor 94 to one input of the parallel in-serialout-register. As shown in FIG. 9B, when the read enable signal (alsoshift/load signal) is a binary 0, the shift register 92 is enabled to beserially shifted. On the other hand, when the read enable (shift/load)signal is a binary 1, the parallel in-serial out-register 92 is enabledto be parallel loaded from the receive data memory register 60. Theactual parallel clocking of data into the parallel in-serialout-register from the receive data memory register is performed with theG48KHZ clock data signal via gates 180 and 184. It will be noted thatthe G48KHZ signal falls in the middle of the read enable 1 pulse. Theset/reset timing of the shift register control flip-flop 174 is shown inFIG. 9B and how that flip-flop controls the application of the G48KHZsignal to the trigger input of the parallel in-serial out-register 92.

When data is serially shifted out of register 92, that data is shiftedin response to the G48KHZ pulses on conductor 186 starting at the timeimmediately following the return of the shift/load signal from a binary1 to a binary 0 as shown in FIG. 9B. As can be seen, the spacing betweenthe read enable 1 signal allows 7 G48KHZ clock signals to be applied tothe parallel in-serial out-register each time a character is shifted outof that register. In other words, for each read enable signal generated,the eight bits in each character residing in register 92 are shifted outin a serial data stream via a conductor 188 and fed to one input of theparity check/generate circuit 166. It is to be noted that thisserialized shifting of data out of the parallel in-serial one-registeris taking place substantially simultaneously with the parallel checkingof the SCU address and the MTU response function code. The obviousreason for the serialized shifting of the data into the parity checkgenerate circuit 166 is so that that circuit can check parity of theentire message coming from the RCC. This type of checking in conjunctionwith the decoding of the message saves time causing the SCU to expediteoverall operations.

After the entire message has been checked, the shift register controlflip-flop is reset from an AND gate 190. That AND gate is enabled as aresult of the ANDING of signals RCE and RCD with the output of AND gate170 receiving the RCA, RCB and RCC signals.

Reference is now made back to the parity check generate circuit 166wherein that circuit, in response to the check parity signal onconductor 164, will generate a parity check fail signal which goes froma binary 0 to a binary 1 if parity of the message in invalid. If theparity check does fail, the parity check fail signal on conductor 192will go to a binary 1 resetting the system control flip-flop via OR gate30, thus immediately placing the SCU back in the standby mode.

Let it now be assumed that the message parity check is valid. In thiscase, the parity check fail signal on conductor 192 remains at a binary0. This signal is applied to an inverter 194 of FIG. 13D via conductors192 and 196, where it is inverted to a binary 1. The output of inverter194 is applied as one input to an AND gate 198 along with the nowpresent check parity signal on a conductor 200 to enable that gate.Since parity is valid, it is now proper to transfer the message from theSCU to the MTU(s) via the SCU's power line. This is accomplished by theenablement of AND gate 194, which applies a binary 1 set signal to the Sinput terminal of a power line transmitter flip-flop 202. As noted inFIG. 9B, the fourth character (parity check) signal is utilized to setthe power line transmitter flip-flop.

With the power line transmitter flip-flop now set, its one outputterminal generates a binary 1 PLXF output signal on a conductor 204. ThePLXF signal, previously a binary 0, now removes an inhibit clear inputfrom a power line control counter 206 of FIG. 13B. With the PLXF binary1 signal now present at the input of the power line control counter, thelatter is enabled to now begin counting at a 30 Hz rate as shown inFIGS. 10A and 10B.

The power line control counter is a six-stage conventional binarycounter generating binary count output signals PLC1-PLC32 on a pluralityof conductors 208. Certain ones of the PLC1-PLC32 output signals areapplied directly to a control counter decode 210 and other ones of thoseoutput signals are applied to three AND gates 212, 214, and 216 viaconductors 218, 220 and 222, respectively. The logic structure of thecontrol counter decode 210 is defined in the following Table 3, which isa listing of Boolean equations defining that structure.

                  TABLE 3                                                         ______________________________________                                        SCU                                                                           POWER LINE CONTROL COUNTER                                                    DECODE EQUATIONS                                                              ______________________________________                                         ##STR1##                                                                      ##STR2##                                                                      ##STR3##                                                                      ##STR4##                                                                      ##STR5##                                                                      ##STR6##                                                                      ##STR7##                                                                      ##STR8##                                                                     ______________________________________                                    

As previously described, before the binary 1 PLXF signal is applied tothe power line control counter 206, that counter is held in the resetstate. Thus, prior to the occurrence of the first 30 Hz signal tocounter 206, a PLC1 binary 1 signal is applied via conductor 218 to ANDgate 212 in conjunction with the 30 Hz signal. These two signals nowenable AND gate 212, which in turn enables an AND gate 224 now receivinga binary 1 SCU RESET signal from the system control flip-flop 28 of FIG.13A. The output of AND gate 224 applies a binary 1 reset signal viaconductors 226 and 228 to two flip-flops SAXFF 230 and GRFF 232,respectively.

Reference is now made to AND gates 214 and 216 of FIG. 13D. A secondinput to each of these AND gates is the now binary 1 PLXF signal on aconductor 234 from the power line transmitter flip-flop 202. Since thatflip-flop is set at this time, these two AND gates are in a condition tobe enabled when their respective input signals PLC8 and PLC16 from thepower line control counter become binary 1's. It will be noted that theoutputs of the two AND gates 214 and 216, designated as RSB2 and RSA2 onconductors 236 and 238, are applied to the two OR gates 102 and 104 ofFIG. 13C.

The RSA2 and RSB2 signals are utilized to enable OR gates 102 and 104 inthe same fashion as previously described for the RSA1 and RSB1 signals.These two signals (RSA2 and RSB2) will generate the proper logic levelsfor signals RSA and RSB on conductors 100 to the receive data memoryregister to effect the proper retrieval of message characters from thatmemory during the transmit sequence of the message. It will be noted atthis time that the two signals PLC8 and PLC16, applied to AND gates 214and 216, are now binary 0's; thus, the RSA and RSB signals applied tothe receive data memory register are likewise binary 0's.

Reference is now made back to the control counter decode 210 (FIG. 13B)now providing a plurality of output signals which are generated at theproper times to effect the serial transmission of the message from thesection control unit (SCU) to the power lines and on to the meterterminal unit(s). In describing the operation of the transmit sequenceof the SCU now under discussion, reference will be made to FIGS. 10A-10Dand 13A-13F and to the previously mentioned Table 3. As previouslydescribed, at the beginning of a transmit sequence, the power linetransmitter flip-flop 202 is set, enabling the power line counter 206 tocount. As shown in Table 3, the first signal to be generated by thecounter decode 210 is an SRTSF (set ready to send flip-flop) signal on aconductor 240. The SRTSF binary 1 signal sets an RTSFF flip-flop 242causing its 1-output terminal to generate a binary 1 RTSF signal onconductor 244 at the time shown in FIG. 10C. The RTSF signal is appliedto an AND gate 246 on a conductor 248. A binary 0 signal DCD (datacontrol delay) on a conductor 250 from an inverter 251 is keeping gate246 disabled at this time because of the binary 1 DCD signal from decode210 (see Table 3). The purpose of the DCD signal will subsequently bedescribed. The RTSF signal is also applied as one input to a transmitAND gate 252 of FIG. 13F. One other input to this latter AND gate is theoutput frequency f₀ of a crystal oscillator 253 in the SCU. It is thisoscillator which generates the high frequency pulse bursts of themessage bits transmitted onto the power line from the SCU.

Reference is now made back to the RTSFF flip-flop 242 of FIG. 13D. Thezero (0) output terminal of that flip-flop is now a binary 0 applying asignal RTSF to an OR gate 254 via a conductor 256. OR gate 254 isdisabled at this time removing a reset input signal from the R terminalof a flip-flop FFDF 258. The binary 0 RTSF signal on a conductor 260also removes a reset signal from the R terminal of a flip-flop FFEF 262.These latter two flip-flops are now in a condition to be set at theproper time.

The next output signal to be generated by the control counter decode 210of FIG. 13B is a 3rd sync bit binary 1 signal on a conductor 264. Theequations for the generation of this signal are shown in Table 3 and thetiming for the generation of that signal is shown in FIG. 10C. As can beseen, the 3rd sync bit signal has a pulse width of one bit time and isgenerated at the count of three by counter 206. The generation of the3rd sync bit signal at this time effects the generation of the 001 syncbits which are appended to the front of the message going to the MTU asshown in FIG. 10C on the data bits XMITD. line. The binary 1 in the 001sync bits is transferred to the power line by the 3rd sync bit signalenabling an OR gate 265 (FIG. 13F). The 3rd sync bit is passed throughOR gate 265 to AND gate 252 via a conductor 267.

Referring to FIG. 13D, the 3rd sync bit signal is also applied to an ANDgate 266 in conjunction with a φD signal from the clock generator 36 ofFIG. 13E, enabling that AND gate to set FFDF 258. Setting FFDF performstwo functions. Its one (1) output terminal now applies a binary 1 signalFFD via conductor 268 to an AND gate 270 of FIG. 13F. AND gate 270 isalso receiving a φB signal to now allow the generation of parity clocksignals for application to the parity check generate circuit 166 throughan OR gate 272 via conductors 274 and 276. The binary 1 FFD signal fromFFDF 258 is also applied via conductor 278 as one input to an AND gate280 of FIG. 13A in conjunction with a φA signal. This latter AND gate isnow enabled to generate a gated 30 Hz signal (G30HZ of 24 pulses) on aconductor 282. As shown in FIGS. 10D and 13D, the FFDF flip-flop whichcontrols the G30HZ signal will be reset after a period of 24 counts by aPL27 signal, thus covering a period of 24 bits to be shifted onto thepower line from the SCU. The G30HZ signal will be applied via OR gate184 to the T input terminal of register 92 to control the shifting ofdata through that register for this 24-bit period.

Reference is now made back to the control counter decode of FIG. 13B andto Table 3. The DCD signal will enable AND gate 246 (still receiving theRTSF signal) when the power line control counter 206 achieves a binarycount of 4 (the end of the three sync bits). The output of AND gate 246is a binary 1 DCT signal on a conductor 284 applied to an AND gate 286in conjunction with serial data coming from the parity check generatecircuit on a conductor 288 (FIGS. 13E, 13F and 13D). It should be notedthat AND gates 246 and 286 are not enabled until the 4th bit of themessage is to be transmitted onto the power line. Simultaneously, the3rd sync bit signal goes to a binary 0. Referring to FIG. 10C, to theline designated data bits XMITD., it can be seen that the 3rd sync bitis transmitted just prior to the first eight message data bitsdesignated SCU fixed address. AND gate 286 is now enabled to allow the24-bit message of serial data to be transferred through that AND gateout to the power lines 18 via OR gate 265, AND gate 252, a power linetransmitter 290 and a power line coupler 292.

Reference is again made back to the control counter decode 210 of FIG.13B to the 3rd sync bit signal line. This signal is also applied via aconductor 294 to an AND gate 296 also receiving the 30 Hz signal. Asshown in FIGS. 10C and 13B, AND gate 296 is enabled with the 3rd syncbit signal to set a flip-flop SAXFF 230. The SAXFF flip-flop nowgenerates a binary 1 signal SAXF on a conductor 298, which is applied toan OR gate 300 to generate a read enable 2 (shift/load) signal on aconductor 302 at the time shown in FIG. 10C. In FIG. 13A, the readenable 2 signal is applied via OR gate 90 to the registers 60 and 92 onconductors 88 and 94, respectively. The first read enable 2 signal isgenerated at the time shown in FIGS. 10C and 13B by the application ofthe 3rd sync bit signal to the SAXF flip-flop via AND gate 296.

It will also be noted that the SAXFF flip-flop is reset one 30 Hz clockafter it is set. This is due to the PLC1 signal going to a binary 1 at acount of 4, thus enabling AND gates 212 and 224 to apply a reset signalto the SAXF flip-flop 230 via conductor 226. This resetting isillustrated in FIG. 10C. The generation of the read enable 2 signal viaOR gates 90 and 300 effects the reading of the first message datacharacter to be transmitted into the parallel in-serial out-register 92.This character is the SCU fixed address on conductors 306 labeled TSCUA.It will be noted in FIG. 13A that the multiplexer 98 receives the SAXFsignal from the SAXFF flip-flop on a conductor 304. The multiplexer 98,which is basically a two-way switch, normally channels data from thereceived data memory register into the parallel in-serial out-register92 when the SAXF signal is a binary 0. As previously mentioned, however,the SCU does not pass on the address which it receives from the RCC, butrather it regenerates its own fixed address for transmission to theMTU(s). This is accomplished by the SAXF signal. With the SAXF signalnow a binary 1, the multiplexer 98 directs the TSCUA signals (SCU fixedaddress) via conductors 306 through the multiplexer into the input ofthe parallel in-serial out-register. The TSCUA signals are clocked intoregister 92 in response to the shift/load and clock data signals onconductors 94 and 186, respectively. As shown in FIG. 10C, when theshift/load signal goes to a binary 1, the TSCUA is parallel loadedthrough the multiplexer into the parallel in-serial out-register. TheSCU fixed address is now shifted out of register 92 as the first eightbits of the message on conductor 188 and applied to the parity checkgenerate circuit 166. These bits of the first character are fed into theparity generate circuit where that circuit monitors these bits and allsubsequent bits of the message in order to generate the proper parity inthe last character of the message. The first character (SCU fixedaddress) is shifted out of the parity check generator circuit as serialdata on conductor 288, and applied to the power lines 18 via AND gate286, OR gate 265, AND gate 252, power line transmitter 290 and the powerline coupler 292.

As shown in FIG. 10C, as soon as the SCU fixed address has been shiftedout of register 92, the second read enable 2 (shift/load) signal isgenerated and applied to registers 60 and 92 via conductors 88 and 94 toload and shift the MTU address to the power line. A third enable 2(shift/load) signal is also generated to load and shift the MTU functioncode onto the power lines. The generation of these two read enable 2(shift/load) signals is described by reference now back to the controlcounter decode 210 of FIG. 13B. The signal which controls the generationof these two read enable 2 signals is a read character signal RCHRcoming out of the control counter decode on conductor 308. Byobservation of Table 3 and of the timing diagram of FIGS. 10A-10D, itcan be seen that the RCHR signal is generated at binary counts of 11 and19. In reality, the count of 11 is actually representative of a count of8 message bits and the count of 19 is representative of 16 message bits.This is due to the necessity of having to count the three sync bitspreviously appended to the front of the message. The first RCHR signalis applied to an AND gate 310 in conjunction with the 30 Hz signal. TheRCHR and 30 Hz signals now enable AND gate 310 to apply a binary 1 setsignal to the S input terminal of the GRFF flip-flop 232. The GRFFflip-flop 1-output terminal now goes to a binary 1 on conductor 316 toenable OR gate 300 to generate the second read enable 2 signal forapplication to registers 60 and 92. As shown in FIG. 10C, the generationof the second read enable 2 signal allows the second character (8-bitMTU address) to be transferred in parallel from the receive data memoryregister via the multiplexer into the parallel in-serial out-register.

It should be mentioned at this time that the SAXFF flip-flop is in thereset state; thus, the SAXF signal is a binary 0 allowing the messagedata to now be transferred through the multiplexer 98 from the receivedata memory register into the parallel in-serial out-register. Since theFFDF flip-flop is still set, the G30 Hz clock pulses are still beingapplied to the parallel in-serial out-data-register via AND gate 280, ORgate 184 and conductors 282 and 186. Thus, the second character isshifted out of register 92 to the power line as previously described.

The addressing of the second character just loaded into register 92 fromthe memory register 60 is effected by the enabling of AND gate 216 withthe PLC8 binary 1 signal on conductor 222 from the power line controlcounter. With the PLC8 signal at a binary 1, AND gate 216 generates abinary 1 RSA2 output signal, which now enables OR gate 104 to provide anRSA binary 1 signal to the receive data memory register. AND gate 214 ispresently disabled, generating a binary 0 RSB 2 output. Thus, OR gate102 is disabled to make the RSB signal on conductors 100 a binary 0.This binary combination of the RSA and RSB signals addresses the secondcharacter location in memory register 60.

Counter 206 will now continue to count, and at a count of 19, the secondRCHR signal is generated. The RCHR signal will again effect the settingof the GRFF flip-flop via AND gate 310 as previously described. Thiswill again cause the generation of the read enable 2 signal to this timeload the third character (function code) from the receive data memoryregister into the parallel in-serial out-register. As shown in FIGS.10A, 10B, 10D and 13D, the addressing of this third character iseffected by the PLC16 signal on conductor 220 from the power linecontrol counter 206 now being a binary 1 and the PLC8 signal being abinary 0. These two signals cause the RSA and RSB signals to becomebinary 0 and 1, respectively, to effect the addressing of the thirdmessage character for transfer from the receive data memory registerinto the parallel in-serial out-register. This third data character isserially shifted out of register 92 on out to the power line aspreviously described.

After transmission of the first three characters (24 bits), the controlcounter decode now generates an output signal designated PL27 (PL27minus 3 sync bits=24 bits). The equation for the generation of the PL27signal is shown in Table 3 and is correspondent with the 24th bit of themessage (see FIG. 10D). The PL27 signal is applied via conductor 318 toAND gate 320 in conjunction with a φD signal to enable that AND gate atφD time to set the FFEF flip-flop 262 and reset the FFDF flip-flop 258via OR gate 254. Resetting the FFDF flip-flop now applies a binary 0signal to AND gate 280 of FIG. 13A, thus disabling the G30 Hz signalbeing applied to the parallel in-serial out-register and preventingfurther shifting of that register. Additionally, when FFDF resets, theFFD signal on conductor 268 goes to a binary 0, disabling AND gate 270of FIG. 13F preventing the φB signals from being applied as parity clocksignals to the parity check generate circuit 166. However, at this time,since FFEF is set, its binary 1 output terminal applies a binary 1signal via conductor 322 to an AND gate 324 of FIG. 13F. The parityclock signals now continue to be generated as a result of thecoincidence between the FFE and the φA signals at AND gate 324. Witheach φA signal, AND gate 324 applies a generate parity clock signal viaOR gate 272 to the input of the parity check generate circuit. In thismanner the necessary clock pulses will be generated to allow the paritycheck generate circuit to generate proper parity in accordance with thatdetermined from the previously transmitted message bits. The paritycheck generate circuit as shown in FIG. 10D will now generate the sixparity bits of the message and place them onto the power lines 18 aspreviously described.

Reference is now made back to the control counter decode 210 of FIG. 13Bfor a description of the last operation performed during the transmitsequence of a message from the SCU to the MTU(s). The signal to begenerated by the control counter decode 210 is a PL34 binary 1 signal.The equations for the generation of this signal are shown in Table 3.The PL34 signal is applied via conductor 326 to an AND gate 152 alsoreceiving the REFF signal from inverter 150. If the function code, aspreviously described, specified that no response is expected from theMTU(s), the REFF signal will be a binary 1 at this time. Thus, the PL34signal will enable AND gate 152 to apply a binary 1 reset signal to thesystem control flip-flop via OR gate 30, placing the SCU back in thestandby mode. The reset timing is shown in the last line of FIGS. 10Cand 10D.

If, however, the function code indicated that a data message response isexpected from the MTU(s) the REFF signal will be a binary 0, disablingAND gate 152 and the SCU will go into a wait mode for receipt of thedata message. This wait mode is accomplished by the application of thePL34 signal via conductor 330 to the input of an AND gate 158 alsoreceiving the binary 1 REFF signal. In this case, if a response isexpected, AND gate 158 will be enabled to apply a binary 1 set signal toa power line receiver flip-flop PLRFF 160 at the time shown in FIG. 10D.

Reference is now made to FIGS. 11A-11H, which show the SCU timing forthe receipt of a data message from one or more MTU's. With the PLRFFflip-flop now set as shown in FIG. 11A, a binary 1 PLRF output signalfrom its 1-output terminal is applied via conductors 332 and 336 to anOR gate 334, which applies a binary 1 reset signal to the power linetransmitter flip-flop 202. The time of resetting this flip-flop is notedin FIG. 11A as the leading edge of the PLRF signal. When flip-flop 202resets, its binary 1 output terminal goes to a binary 0 disabling ANDgates 214 an 216 and replacing the inhibit/clear signal on the powerline control counter. Counter 206 is now reset in preparation to receiptof the next message from the RCC. Resetting counter 206 causes the DCDsignal on conductor 250 to go to a binary 0, thus preventing any furthertransmission of message data through AND gate 286 to the power line.This now frees the SCU to receive data messages via the power linecoupler 292.

Referring now to FIG. 13B, the PLRF signal is also applied to aplurality of receivers 338 and to a common data path switch 340 in apower line receiver common logic block 342. The PLRF signal in essencesimultaneously turns on all receivers 338 and enables switch 340 forreceipt of data from the power lines 18 via the power line coupler 292,conductor 344, and conductor 346. After an MTU(s) has decoded thefunction code of its received message as a transmit data command, itwill serially transmit the meter data onto the power lines for receiptby the SCU. The serialized meter data appears at switch 340 afterpassing through coupler 292 and is transferred therethrough atfrequencies f₁ through f₈, with each frequency corresponding to aseparately addressed MTU. The meter data on conductor 346 is applied incommon to all of the receivers 338. Each receiver will accept only themeter data being received at its tuned frequency (one of f₁ -f₈). Thetiming signals for controlling the transfer of data into the receiversand to the RCC are controlled by a plurality of clock signals D_(e) A,D_(e) B and D_(e) C generated by common logic 342 on conductors 348, 350and 352, respectively. The common logic 342 also receives a strobesignal from each of the receivers 338 via conductors 354 and 356 when areceiver detects the receipt of a message of meter data. The meter datais transferred in parallel from each of the receivers via conductors 554to the data transmitter receiver 40. The D_(e) C signal clocks the meterdata into the transmitter receiver, which transfers that data to the RCCvia the transmitter 162.

SCU RECEIVER OPERATIONAL DESCRIPTION

Reference is now made to FIG. 14, which is a legendary drawing showingthe inter-relationships between FIGS. 14A through 14D. In order tofollow the operational description of the receiver portion of the SCU,it is recommended that FIGS. 14A through 14D be organized as shown inaccordance with FIG. 14. In a similar fashion, it is recommended thatFIGS. 11A-11H be positioned in accordance with the legendary drawing ofFIG. 11.

The previously mentioned power line receiver common logic 342 isillustrated in detailed block diagram form in FIGS. 14C and 14D. Each ofthe previously mentioned receivers 338 in FIG. 13B is similar with theexception of their ability to receive data messages from the MTU's at aspecified frequency for a particular MTU. Since all of the receivers 338are substantially the same, the operation of only one of those receiverswill be described. The detail logic for a typical one of the receivers338 is shown by FIGS. 14A and 14B.

Reference is now made to FIGS. 11A-11H. FIGS. 11A and 11B show the basictiming of the various clock pulses provided to the receiver logic fromthe master clock generator 36 of FIG. 13E. FIGS. 11C and 11D illustratethe timing of a typical one of the receivers 338, which is receivingmessage data from the power line. In the illustrated embodiment, it willbe recalled as previously described in connection with FIG. 1, that asmany as eight MTU's can be transmitting information onto the power linesimultaneously. Because of various delays in the system caused, forexample, by the physical displacement of MTU's along the power line andthe turnaround or response time in each of the various MTU's to receivedmessages, the message data from each of eight addressed MTU's may notreach the SCU at exactly the same time. For this reason, the SCU must becapable of insuring that the first message received from an MTU and thelatest message received from an MTU is captured by the SCU andtransferred to the RCC. In FIGS. 11C and 11D, it will be noted that thattiming diagram specifies the receipt of the earliest power line datafrom a receiver #1, which could be any one of the receivers 338. FIGS.11G and 11H are somewhat similar to FIGS. 11C and 11D; however, FIGS.11G and 11H show the operation of a receiver #N, which can be any one ofthe receivers 338, receiving the latest power line data from an MTU. Thepower line receiver common logic timing is illustrated by FIGS. 11E and11F.

In the ensuing description, the receiver operation will be described byfirst assuming that a message has been transmitted onto the power lineby an SCU to address only one MTU on that power line. Thus, that one MTUwill be the only one to respond with a data message back to the SCU. Inthis particular instance, that message could be considered to be theearliest power line data illustrated by the timing diagram of FIGS. 11Cand 11D. The common logic for the receiver as illustrated by FIGS. 11Eand 11F will also be described in connection with this one addressedMTU. Following that description, the operation of the receiver logicwill be described, utilizing FIGS. 11G and 11H with the assumption thata message transmitted to the MTU's is a message which addresses aplurality of MTU's (e.g., eight MTU's) to transmit their meter datasimultaneously to the SCU. In this particular instance, the descriptionof FIGS. 11G and 11H will entail the receipt of an SCU of the latestdata from one of the addressed MTU's. FIGS. 11E and 11F will also bedescribed in connection with FIGS. 11G and 11H.

Reference is now made to FIG. 14C. In that figure the PLRFF flip-flop160 has been re-illustrated as a portion of the power line receivercommon logic 342 to make it easier to understand the overall operationof the power line receiver logic.

As previously described in connection with FIG. 13B, the primary purposeof the PLRFF flip-flop is to turn the power line receivers on and off.Let it first be assumed that the PLRFF flip-flop is in a reset state. Asa result, its zero output terminal is generating a binary 1 PLRF signalon conductor 358. The PLRF signal is utilized to keep each of thereceivers and the receiver common logic in the reset, or off, state whena message is not to be received from an MTU(s). A plurality offlip-flops, φ AF/F 360, φ BF/F 362, φ CF/F 364, and φ DF/F 366 are allheld in the reset state by the PLRF signal applied to the resetterminals of those flip-flops via a conductor 368. The PLRF signal islikewise applied on a conductor 370 to a reset R terminal of a removestart bits discounter 172 to reset that counter and simultaneouslyinhibit it from counting. Three other flip-flops, F/F1A 374, F/F2A 376,and EOMF/F 378 of FIG. 14D, are likewise held in the reset state by thePLRF signal on a conductor 380. Further, a flip-flop 50MSF/F 382 is heldin the reset state by the PLRF signal's being applied to the resetterminal of that flip-flop via an OR gate 384 and conductors 386 and388. Additionally, a message length counter 390 is inhibited fromcounting and held in the reset state by the PLRF signal on conductor 392being applied to a reset input terminal of that counter. A 30 Hz strobeclock counter 394 is held in the inhibited reset state indirectly by thePLRF signal, which resets flip-flop 376 to apply a binary 1 signal fromits zero output terminal via a conductor 396 and an OR gate 398 to thereset terminal of counter 394. In a similar fashion, a 50 MS delaydivide by 12 counter 400 is held in a reset inhibit count stateindirectly by the PLRF signal from the zero output terminal of flip-flop374 via conductors 402 and 540.

Referring to FIG. 14C, the PLRF signal is also applied to a resetinhibit input terminal of a 267 MS delay divide by 8 counter 404 on aconductor 406 holding that counter in a reset inhibit count state. Fouradditional flip-flops, a 25 MS Delay Control flip-flop 408, a STATE F/Fflip-flop 410, a STORE A flip-flop 412, and a STORE B flip-flop 414 ofFIG. 14B are also held in the reset state by the PLRF signal. It will benoted that the PLRF signal applied to the reset input terminal of eachof these latter flip-flops is the complement of the binary zero PLRFsignal now present at the one output terminal of the PLRF flip-flop 160on conductor 416. The PLRF signal on conductor 416 is inverted throughan inverter 418 to the PLRF binary 1 signal on conductor 420. An OR gate422 passes the PLRF signal to the reset R input terminal of flip-flop410 via conductor 424. In a similar manner, the PLRF signal is appliedto the reset input terminal of flip-flop 408 via conductors 426, 428 andan OR gate 430. Flip-flops 412 and 414 are reset by the PLRF signal frominverter 418 via conductors 432 and 434 applied to reset input terminalsof those flip-flops.

As previously described, the receivers illustrated by FIGS. 14A and 14Bare representative of a one of the plurality of receivers 338 in theSCU. As shown in FIG. 14C, the PLRF and PLRF signals are provided to allother power line receivers in the SCU in the same manner as just shownand described in connection with FIGS. 14A-14D. The PLRF and PLRFsignals are shown going to all of the other receivers (not shown) onconductors 436 and 438, respectively. Also, for a more easyunderstanding of the description of the SCU receivers, the data messageswitch 340 has been duplicated in FIG. 14C receiving the PLRF signal viaconductors 416 and 440.

Prior to proceeding with a further description of the SCU receiveroperation, it is considered advantageous to reconsider the messageformat of FIG. 4 showing the format of meter data which is received bythe SCU from any one of the MTU's. As shown in FIG. 4, that message iscomprised of 45 bits, of which the first three bits are the sync, orstart, bits and 42 bits comprise meter data and parity. This message isreceived by the SCU in the order shown in FIG. 4 from the left to theright, starting with the three sync bits.

Let it now be assumed that the SCU has just decoded a command andtransmitted it to an addressed MTU that specifies that the MTU is totransmit meter data back over the power lines to the SCU. As such, thePLRF flip-flop 160 is in the set state, placing the SCU in a messagereceive wait mode by removing the previously described reset signalsfrom the various flip-flops and counters in the receiver logic. This hasthe effect of basically turning on all of the receivers simultaneouslyin preparation to the receipt of a message from the addressed MTU. Aspreviously mentioned, the operation of the receivers will first bedescribed with the receipt of a message from a single MTU.

Reference is now made to FIG. 14C to the data input (f₁ -f₈) onconductor 344 coming into switch 340. Since the PLRF flip-flop is nowset, switch 340 is enabled by a binary 1 PLRF signal on conductor 440applied to that switch. As soon as the meter data arrives at the SCUfrom the MTU, it will be passed through switch 340 via conductor 346 andapplied to a narrow band receiver/amplifier circuit 442. The messagedata is amplified in receiver amplifiers 442 and provided to the inputof a band pass commutating filter 444 via conductor 446. It will berecalled that the MTU is capable of transmitting its metered data at itsown specified frequency. These frequencies were previously described asf₁ -f₈. Further, it was also pointed out that the SCU is capable ofreceiving in each of its receiver circuits a meter data message at thefrequency corresponding to that being transmitted by one of the MTU's.In FIG. 14A there is shown an f_(x) crystal oscillator 448 providing anf_(x) RF signal on a conductor 450 to one input of the band passcommutating filter 444. The frequency of the f_(x) signal on conductor450 can be representative of any one of the previously mentionedfrequencies f₁ -f₈, depending upon which receiver is being considered.The purpose of the band pass commutating filter 444 is to allow thereceiver to receive only the message data corresponding to thatfrequency f_(x) by filtering out all unwanted frequencies and passingthe message data out of the filter 442 corresponding to the desiredmessage.

Reference is now made to the top lines of FIGS. 11C and 11D designatedearliest power line data (receiver #1) and one-shot #1 (10 MS). Tounderstand the operation of the receivers of the SCU, it is important torealize that in the present system, the presence of a pulse burst ofenergy on a power line is representative of a binary 0, whereas theabsence of a pulse burst is representative of a binary 1. As shown inFIG. 11C, the first three bits of information from the MTU entering theSCU receiver of FIG. 14A are the three sync bits designated S1, S2 andS3. It will also be noted that the message data transferred over thepower lines between the MTU and SCU and from the SCU to the MTU is at a30 Hz rate; thus, the pulse spacing between each of the data bits in themessage is 33.3 milliseconds as shown in FIG. 11C. As shown in FIG. 11C,the power line data is normally at a binary 1 state and when a pulseburst (binary 0) is placed on the power line by the MTU, the output ofthe band pass filter 444 will generate a negative signal as shown in theearliest power line data line of FIG. 11C. This negative going pulse isapplied via a conductor 452 to a trigger (T) input of a one-shot, 10millisecond multivibrator 454. The output of multivibrator 454 is shownin FIG. 11C on the one-shot #1 line as two pulses corresponding to thefirst two binary 0 sync bits and the absence of a pulse shown as adotted or phantom pulse representative of the binary 1 sync bit. Allmessage bits following the three sync bits are shown in cross-hatchedform as those bits are indeterminate, dependent upon the contents of themessage. These cross-hatched bits are shown as data bits 1 through 42.For each data bit which is a binary 0, one-shot 454 will be fired togenerate a 10 millisecond output pulse as shown in FIG. 11C. The databits from the output of one-shot 454 are applied to an AND gate 456 viaa conductor 458.

The other input to AND gate 456 is a binary 1 signal on a conductor 460from the output of an inverter 462. Inverter 462 is presently receivinga binary 0 output signal from an OR gate 464 now disabled. This isexplained as follows: Prior to the reception of a message from the MTU,the four flip-flops 360 through 366 are in the reset state. Thus, theirbinary 1 output terminals are each providing a binary 0 signal onconductors 466 to the output of OR gate 464. Thus, it can be seen thatwith the appearance of the very first sync bit in the message, AND gate456 will be enabled to apply a binary 1 signal as one input to each offour AND gates 468, 470, 472 and 474 via a conductor 476. The secondinput to these AND gates are the φA through φD signals from the masterclock generator 36 of FIG. 13E.

Reference is now made to FIGS. 11A and 11B, which illustrate the timingrelationships between the φA through φD signals. It will be noted thatthere are four phase signals (φA through φD) generated for each bit timeof the incoming message. This is seen by comparing the φA through φDsignals with the pulse width of the 30 Hz signal shown in FIG. 11A. Thereason for the φA through φD signals and the circuitry in FIG. 14A is tobe able to synchronize the clocking of the data bits into the receiverwith a 30 Hz clock signal. The majority of the circuitry shown in FIG.14A comprises basically a strobe sync detector circuit for developingthe just-mentioned synchronization. As will be seen, this circuitry iscapable of synchronizing any one of the 30 Hz φA through φD signals withthe 30 Hz incoming data to generate a synchronization strobe A signalshown in FIGS. 11C and 11D.

As shown in FIG. 11C, it will be noted that one-shot 454 generates thefirst sync pulse output signal approximately in the middle of the φBsignal. Referring now to AND gate 470 of FIG. 14A, the coincidencebetween the first sync bit on conductor 476 and the φB signal applied toAND gate 470 enables that AND gate to apply a binary 1 set signal to theinput of the φB F/F 362. FIG. 11C shows the setting of the φB F/F #1 onthe leading edge of the output of one-shot #1. The one-output terminalof the φB F/F 362 is connected via a conductor 478 as one input to anAND gate 480. The other input to AND gate 480 is the φC signal on aconductor 482. With the φB F/F now set, the first φC signal followingthe setting of that flip-flop will enable AND gate 480 to generate abinary 1 output signal on a conductor 484 to an OR gate 486. The OR gate486 now passes its input signal, via a conductor 488, to an AND gate490. The other input to AND gate 490 is presently a binary 1 signal froman inverter 492 now receiving a binary 0 input on conductor 494 fromdisabled AND gate 496.

AND gate 496 is connected to the output of the remove start bits counter372 and decodes the output of that counter to generate a binary 1 signalon conductor 494 when the counter reaches a count of three. At thepresent time this counter is zeroed out; thus the output of AND gate 496is a binary zero, causing inverter 492 to apply a binary 1 enable signalto AND gate 490. Reference is now made back to FIGS. 11C and 14A, whichshow the start bits strobe #1 being applied to the trigger T input ofcounter 372 via conductor 498. It will be noted that the start bitsstrobe coincides with the φC signal applied to AND gate 480.

It will be noted in FIG. 14A that when the φB F/F 362 sets, itsone-output terminal provides a binary 1 signal on one of the conductors466 to OR gate 464. This binary 1 signal is passed through OR gate 464and inverted to a binary 0 signal by inverter 462, thus applying adisable input signal to AND gate 456 via conductor 460. Disabling ANDgate 456 applies a binary 0 disable signal to each of the AND gates 468through 474. Since these AND gates are disabled, those AND gates can nolonger apply set signals to any of the other flip-flops 360 through 366.It is significant to note that the circuit of FIG. 14A is capable ofsynchronizing any one of the φA through φB signals with the first dataor sync bit coming into the receiver. Further, it will be noted thatwhenever a particular one of the φA through φD flip-flops is set, thestrobe A signals will be generated at the phase (φ) signal immediatelyfollowing that which set the particular flip-flop. In the example shownin FIGS. 11A through 11D, the φB flip-flop is set at φB time and thestrobe A (#1) signals are generated at φC time, thus locking in thesystem to generate the strobe A signal with each φC signal. If the firstsync bit (S1) had happened to coincide, for example, with the φA signal,AND gate 468 would have been enabled to set flip-flop 360. This wouldcause the binary 1 output of the φA F/F 360 to enable an AND gate 506 tobegin generating the start bits strobe and the strobe A signals at φBtime.

Reference is again made to FIG. 11C to the start bits strobe #1 line. Itis seen that three sync, or start, strobe signals are generated by ANDgate 490 and applied to counter 372 (FIG. 14A). When counter 372 reachesa count of three, AND gate 496 is enabled to apply a binary 1 signal asone input to an AND gate 500 on a conductor 502. The binary 1 signal isalso applied to inverter 492, which now disables AND gate 490 preventingapplication of the start bits strobe to the cohnter 372. It will benoted that the output of OR gate 486 is also connected as one input toAND gate 500. AND gate 500 will now begin to generate the previouslymentioned strobe A signal on a conductor 504 in response to each φCsignal as shown in FIGS. 11C and 11D on the strobe A(#1) line. Thestrobe A signal on conductor 504 is applied as one input to an AND gate508, which is now enabled by the binary 1 PLRF signal also applied tothat AND gate. The output of AND gate 508 is utilized to strobe or clockthe meter data from the MTU into a STORE A F/F 412 via a conductor 510.The serialized message data from one-shot 454 is also applied to a dataterminal D of flip-flop 412 via conductor 512. Referring to FIG. 11C, itcan be seen that the strobe A (#1) signal at φC time always falls incoincidence with the output of one-shot, #1 454. If one-shot 454 isgenerating a binary 1 output signal, the strobe A signal on conductor510 will cause flip-flop 412 to set. If the output signal from one-shot454 is a binary 0, flip-flop 412 will reset. In this manner, binary 1'sand 0's are shifted from the power line into the data receiver flip-flop412.

The output of AND gate 508 is also applied to an OR gate 514 via aconductor 516. For each strobe A signal generated by AND gate 508, ORgate 514 passes that signal to a trigger T input terminal of the 25 MSdelay control flip-flop 408 causing that flip-flop to set at a time asshown in FIG. 11C on a 25MSD (#1) line. Flip-flop 408 sets at this timecausing its 0 output terminal to go to a binary 0 state on conductors518 and 520. With the 0 output terminal on conductor 518 toing to abinary 0 at this time, it has no effect on the state flip-flop 410.However, the binary 0 signal 25MSD on conductor 520 is applied as arelease input signal to an R terminal of the 25 MS delay counter 522.This removes the reset inhibit input to counter 522, allowing thatcounter to begin to count 120 Hz pulses. At the end of the count ofthree by counter 522, it generates a 25 millisecond delay output signalCT3 on a conductor 524. The Ct3 signal enables OR gate 514 to againtrigger flip-flop 408, causing it to reset. Resetting this flip-flop 408results in applying a binary 1 signal back to the R input of counter522, thus zeroing out that counter and inhibiting it from counting.Further, the binary 1 signal causes the STATE F/F 410 to now set at thetime shown in FIG. 11C on the STATE F/F (#1) STATE line. With flip-flop410 now set, its 0 output terminal generates a binary 0 output signalSTATE on a conductor 526 to disable an AND gate 528.

The binary 1 output of flip-flop 408 on conductor 518 is also applied atthis time to a trigger (T) input signal of a STORE B flip-flop 414 via aconductor 530. As shown in FIG. 11C, the binary 1 25MSD signal causesthe previously stored data bit from flip-flop 412 to now be clocked intothe STORE B flip-flop 414 via a conductor 532 applied to a data D inputterminal of that flip-flop. Simultaneously with the clocking of thepreviously stored data bit from flip-flop 412 into flip-flop 414, thenext data bit is strobed into flip-flop 412. This is always done on theleading edge of the STROBE A signal as shown in FIG. 11C.

Reference is now made back to FIG. 14A to the output of AND gate 500generating the strobe A signal on conductor 504. It is shown there thatthe strobe A signal is also applied via a conductor 534, as one input toan OR gate 536 of FIG. 14D. It is significant to note at this time thatOR gate 536 receives a strobe A input from each of the plurality ofreceivers in the SCU. The reason for this is explained as follows: Inorder to properly clock all of the message data from the MTU's into theSCU receivers, it is desirable to develop the sync bits and strobe Asignals from the first sync bit of the first, or earliest, incomingmessage from the MTU's. The detection of this first sync bit, aspreviously described, effects the starting of the strobe A signals onconductor 534. Once that first strobe A signal has been generated, it isnecessary to block out all of the other receivers from providing strobeA signals to the common power line receiver logic in FIGS. 14C and 14Dso that all data will be clocked into the plurality of receiverssimultaneously under control of one strobe A signal.

As shown in FIG. 14B, when OR gate 536 is enabled, it simultaneouslyapplies a binary 1 signal on a conductor 538 to a set input terminal ofthe FF1A flip-flop 374 and the 50 MS flip-flop 382. This binary 1 signalcauses both of those flip-flops to set, generating a binary 0 outputsignal from each one's 0 output terminal. The timing for the F/F1A and50 MS F/F is shown in FIGS. 11E and 11F. The binary 0 output signal fromflip-flop 374 is applied as an inhibit signal via conductors 540 and 542to an inhibit terminal shown as a circled inverter on the input of ORgate 536. This inhibits the passage of strobe signals from any of theother receivers through OR gate 536. As shown in FIGS. 11E and 11F, theFF1A flip-flop will remain in the reset state until the complete messagehas been received, at which time it will be reset. This will bedescribed subsequently.

Reference is now made back to the set S input terminal flip-flop 382.Flip-flop 382, which is now set, generates a binary 0 signal from its 0output terminal on a conductor 544. This signal is applied to a set Sinput terminal of a flip-flop FF2A 376. As shown in FIG. 11E, thissignal has no effect on the operation of that flip-flop at this time.Referring now to FIG. 14D, it will be noted that the binary 0 outputsignal from flip-flop 374 is also applied as a release signal onconductors 402 and 540 to an R input terminal of the 50 milliseconddelay divide by 12 counter 400. Counter 400 now begins to count 120 Hzinput clock signals applied to the trigger T input terminal of thatcounter. The output signals of counter 400 are applied via a pluralityof conductors 546 to the input of a 50 MS divide by 12 decode network548. As shown in FIG. 11E, after a 50 millisecond delay, the decodenetwork 548 will generate a binary 1 output signal on a conductor 550,which is passed through OR gate 384 via conductor 388 to reset the 50 MSF/F 382. Resetting flip-flop 382 now causes the 0 output terminal ofthat flip-flop to go to a binary 1 on conductor 544, thus setting F/F2A376 as shown in FIG. 11E. With flip-flop 376 now set, its 0 outputterminal now goes to a binary 0 on conductor 396 to now apply a binary 0release signal to the R input terminal of the 30 Hz strobe clock counter394 via OR gate 398.

Counter 394 now begins to count 240 Hz input pulses applied to the Tterminal of that counter. The output stages of that counter designatedCCB, CCC and CCD are applied via their corresponding output lines to theinput of a clock decode 30 Hz generator circuit 552. Decode 552 alsoreceives the 240 Hz input pulses via a conductor 554. The equationsdefining the internal decode logic of decode 552 are given on the timingdiagram of FIG. 11E on the lines D_(e) A, D_(e) B and D_(e) C. It willbe noted in FIG. 11E and 14D that the D_(e) A, D_(e) B and D_(e) Csignals are sequentially generated by the decode 552.

The generation of the first D_(e) A signal in the present descriptionhas no effect on the operation receiver. However, it will be noted asshown in FIGS. 11E and 11C that the leading edge of the first D_(e) Bsignal from the output of decode 552 is applied as a binary 1 signal toOR gate 422 of FIG. 14B via conductor 350. OR gate 422 now passes theD_(e) B signal to the reset input terminal of flip-flop 410 viaconductor 424. This causes the STATE F/F 410 to now reset generating abinary 1 STATE output signal on conductor 526 to AND gate 528. It willalso be noted at this time that the 25 MS delay control flip-flop 408 isagain triggered to reset at the count of three (CT3) applying a setsignal to the STATE F/F 410, causing that flip-flop to immediately setas shown in FIG. 11C.

It is significant to note that the D_(e) A and D_(e) B signals as shownin FIG. 14D are also applied to all of the power line receivers 338,causing those receivers to all operate in the same fashion as justdescribed in connection with FIGS. 14A, 14B, 14C and 14D. Referring nowback to FIG. 14D, the next output signal to be generated from the decode552 is the D_(e) C signal on a conductor 352. That signal is shown beingdeveloped as an output signal from the power line receiver common logic342 in FIGS. 14D and 13B for application to the datatransmitter/receiver circuit 40. It is this D_(e) C signal which effectsthe parallel transfer of data from each of the eight receivers (FIG.13B) into the data transmitter/receiver 40.

Referring back to FIG. 14B, it will be recalled that each data bit whichis strobed into the STORE B flip-flop is transferred via a one of theplurality of conductors 554 from the corresponding receivers to theinput of the data transmitter/receiver 40 shown at 8 data lines in FIGS.13A and 13B. As each data bit from the receivers is transferred to thedata transmitter/receiver 40, it is necessary to keep track of thenumber of bits in the message, which have been transferred. This iseffected by the CCD signal generated by the clock counter 394 in FIG.14D. The timing for the generation of the CCD signal is shown in FIGS.11E and 11F, whereby the leading edge of that signal triggers a messagelength counter 390 with a binary 1 signal on a conductor 556. As shownin FIGS. 11E and 11F, the message length counter 390 is counted up byone in response to each CCD pulse. The message length counter outputstages are provided via a plurality of conductors 558 to a messagelength decode 560, which generates an output signal CT42 on a conductor562 when the message length counter achieves a count of 42. Thegeneration of the CT42 signal is shown in FIG. 11F. The CT42 signal,upon the detection of the 42nd count, or 42nd message bit, (see FIG. 4)is applied as a binary 1 set signal to an end of message flip-flop EOMF/F 378 via conductor 562. As shown in FIG. 11F, the CT42 signal causesthe EOM F/F to set, thus generating a binary 1 EOM signal from the 1output terminal on a conductor 564. The EOM signal on conductor 564 isapplied to the input of OR gate 30 of FIG. 13A, causing the systemcontrol flip-flop 28 to reset, thus generating the binary 1 SCU resetoutput signal on conductor 34 to completely reset the entire SCU inpreparation to receipt of another message from the RCC.

It should also be pointed out that each message bit transferred to thedata transmitter/receiver 40 of FIG. 13A by the D_(e) C signal isstrobed through the transmitter modulator 162 for transfer to the RCCprior to the transfer of the next data bit from the receiver. Referringback to FIG. 14D, it will also be noted that the CT42 signal from decode560 is applied on conductor 562 to OR gate 398 to immediately resetcounter 394 after it has generated the last CCD signal shown as a veryshort signal in FIG. 11F. Referring to FIG. 13B, it will be noted thatthe SCU reset signal is now applied to the PLRFF flip-flop 160. ThePLRFF flip-flop will now reset as shown in FIG. 11B, causing thatflip-flop to generate a PLRF binary 1 signal on conductor 358 as shownin FIG. 14C to reset the entire receiver section in the manner aspreviously described at the outset of this discussion.

The operation of the SCU receiver section will now be described with theassumption that the message command previously transmitted to the powerlines addresses eight MTU's and specifies in its function code that allof the MTU's are to simultaneously transmit their meter data over thepower lines 18 to the SCU. These eight messages will each be at adifferent frequency and will be received by the eight receiverscorresponding to the frequency of each of the messages from theaddressed MTU's. It will be recalled, as previously mentioned, becauseof inherent delays in the system, that the data from several MTU's maynot arrive simultaneously at the SCU. This non-simultaneous arrival ofinformation at the SCU receiver section from the plurality of MTU's isillustrated in the timing diagrams of FIGS. 11C, 11D, 11E, 11F, 11G and11H. FIGS. 11G and 11H, in particular, illustrate the latest power linedata being received by a one of the receivers designated receiver #N inFIG. 11G approximately 40 milliseconds after receipt of the earliestpower line data being received by receiver #1 as shown by FIGS. 11C and11D. To understand the operation of the plurality of receivers receivingthe earliest and latest data, it is necessary to visualize that thereceiver of FIGS. 14A and 14B is representing a receiver (receiver #1)receiving the earliest power line data, as well as another receiver(receiver #N) receiving the latest power line data.

Let it now be assumed that all MTU's have been commanded to transmittheir meter data over the power lines 18 to the SCU. The first receiverto receive the first sync or start bit of the SCU message is illustratedby the earliest power line data (receiver #1) timing diagram of FIGS.11C and 11D. The operation of receiver #1 has already been described inconnection with the timing diagrams of FIGS. 11A-11F and will operate inthe same manner as previously described. However, it will be noted thatthe receiver #N receiving the latest power line data illustrates certaindifferences in the timing in FIGS. 11G and 11H compared to thatpreviously described in connection with FIGS. 11C and 11D of receiver#1.

Referring to FIGS. 14C and 14D, it is significant to point out, aspreviously described, that the power line receiver common logic willalways select the first strobe A signal generated by the receiverreceiving the earliest power line data. When this occurs, OR gate 536 isinhibited from receiving the strobe A signal from any other receiverlater receiving data from an MTU. Let it now be assumed that thereceiver illustrated in FIGS. 14A and 14B is that shown by the timingdiagram of FIGS. 11G and 11H receiving the latest data. It will be notedthat the strobe A #N signal is generated in the same manner aspreviously described for the strobe A #1 signal. However, forillustrative purposes, it is shown that the strobe A #N signal is beinggenerated at φA time instead of φC time as previously described inconnection with FIGS. 11C and 11D. This was done merely to show how anyreceiver can lock in on any one of the φA-φD pulses. The operation ofthe remove start bits counter 372 in FIG. 14A to stop that counter atthe end of three start bits strobes and to enable AND gate 500 is thesame as previously described in connection with FIGS. 11C and 11D. Aspreviously described, the first strobe A signal (#N) will simultaneouslyclock the first data bit (latest received data bit) into the STORE A F/F412 and trigger the 25 millisecond delay control flip-flop 408, causingthat flip-flop to go into a set state generating a binary 0 25MSD signalon conductor 520. The next significant action to note is that the firststrobe A signal generated by receiver #1 at φC time has effected thestarting of the 30 Hz strobe clock counter 394 to begin the generationof the D_(e) A, D_(e) B and D_(e) C signals after the 50 milliseconddelay (50 MSF/F) as shown in FIGS. 11E and 11F. It will be noted at thistime that the STATE F/F 410 as shown in FIG. 11G is in a reset state,thus generating a binary 1 STATE signal on conductor 526 to now enableAND gate 528 to be enabled upon the occurrence of the D_(e) A signal. Asshown in FIGS. 14B, 11E, 11F, 11G, the leading edge of the D_(e) Asignal on conductor 348 causes AND gate 528 to be enabled, generating abinary 1 output signal on conductor 566. This latter signal is passedthrough OR gate 430 to now set the 25 millisecond delay controlflip-flop 408 at a time as shown on the 25MSD (#N) line of FIG. 11G.With flip-flop 408 now reset, its binary 0 output terminal goes to abinary 1 on conductor 518, causing flip-flop 410 (STATE F/F #N) to set,disabling AND gate 528. However, flip-flop 410 will immediately be resetat leading edge of the D_(e) B signal as shown in FIGS. 11G, 14B and14D, in preparation for the repeated cycle of the 25 millisecond delayand STATE F/F (#'s N) operations as just described.

By comparing the timing of the 25MSD signals shown in FIGS. 11G and 11C,it can be seen that this timing allows the data in the latest power linereceiver #N to be clocked into its STORE A F/F 412 and from thatflip-flop into its STORE B F/F 414 prior to the occurrence of the D_(e)C signal shown in FIG. 11E, so that the latest received data is in thebuffer store flip-flop 414 of all receivers in time to be simultaneouslytransferred from the receivers via conductors 554 (FIG. 13B) into thedata transmitter/receiver 40 for transfer to the RCC via the transmittermodulator 162.

By referring to FIGS. 11D, 11F and 11H, it can be seen that the 42nddata message bit from each MTU is clocked from the eight receivers intothe data transmitter/receiver 40 for transfer to the RCC upon theoccurrence of the last D_(e) C pulse appearing in FIG. 11F. Immediatelyfollowing the shifting of the 42nd data bit out of the SCU to the RCC,the CCD signal as shown in FIG. 11F causes the message length counter tobe triggered to generate a count of CT42 from decode 56 to thus set theEOM F/F 378. The EOM F/F, now generating the EOM binary 1 signal onconductor 564, will effect a complete total reset of the SCU in the samemanner as previously described, thus preparing the SCU for receipt ofanother command from the RCC.

One remaining portion of the SCU remains to be explained. Reference isnow made to FIGS. 12, 14C and 14D. There may be circumstances whereby anMTU or MTU's do not respond to a message transmitted to those units froman SCU. These may be situations where an invalid function code or aninvalid address is transmitted to MTU(s), in which case the MTU(s) willnot respond with a message back to the SCU. If the SCU is in the waitmode, expecting a message response from the MTU(s), that unit will hangup in the wait mode until a message is received. In order to prevent theSCU from hanging up in this mode, a provision has been made whereby, ifa message is not received within a specified period of time, the SCUwill automatically send a message of, for example, all binary 1's or allbinary 0's, to the RCC. This message can be recognized by the program inthe RCC as an invalid message. The SCU will reset after that message istransferred to the RCC.

Referring to FIG. 14C, let it now be assumed that the PLRFF 160 is in aset state. With PLRFF 160 in a set state, the PLRF signal applied to the267 millisecond delay counter 404 via conductor 406 is a binary 0enabling the counter to begin counting the 30 Hz signals applied to anAND gate 570. AND gate 570 is enabled by the binary 1 FF2A signal fromflip-flop 376 via conductor 572. The timing for the operation of the 267millisecond counter 404 is shown in FIG. 12 on the 267 MSD line. It willbe noted that after 267 milliseconds, an AND gate 574 decoding outputsignals on conductors 576 from counter 404 generates a 267 MSD binary 1signal when that gate detects a count representative of a 267millisecond delay. The 267 MSD signal is simultaneously applied to apreset input PR of flip-flops 374 and 376 via a conductor 578. As shownin FIG. 12, the two flip-flops FF1A 374 and FF2A 366, when set by the267 MSD signal, will generate binary 0 output signals on theircorresponding conductors 540 and 572. The binary 0 signal from the 0output terminal of FF2A now allows the output of OR gate 398 to go to abinary 0 signal releasing the 30 Hz strobe clock counter 394 to begincounting the 240 Hz clock signals. As can be seen in FIG. 12, the clockdecode 552 of FIG. 14B will now begin to generate the D_(e) A, D_(e) Band D_(e) C signals in the same manner as previously described. TheD_(e) A and D_(e) B signals are applied to all of the power linereceivers; however, those two signals have no effect on any of thereceivers because a message has not been received by any of thosereceivers to effect the generation of a strobe A signal, which startsthose receivers into operation. The one signal which is significantcoming out of the clock decode 552 in this particular instance is theD_(e) C signal on conductor 352. That signal, as previously described,is applied to the data transmitter receiver 40 of FIG. 13A via conductor352 to parallel transfer the information from the STORE B F/F 414 ineach of the receivers onto the trunk line 14 going to the RCC from thetransmitter modulator 166. The information transferred to thetransmitter receiver 40 will be either binary 1's or binary 0's,dependent upon the state chosen for the STORE B F/F 414. The state ofthe STORE B F/F is shown in the example of FIG. 14B to be reset at alltimes, except when data is being received from the STORE A F/F 412. Inthis example, all binary 0's would thus be transferred to the RCC as aninvalid message for use by the program. However, if the design sodictates that all binary 1's are to be transferred to the RCC, the STOREA F/F 412 would merely have to be in the set state to effect thetransfer of all binary 1's from the STORE B F/F to the RCC.

Referring again to FIGS. 12 and 14D, it can be seen that the CCD signalwill cause the message length counter 390 to count each bit beingtransferred (each D_(e) C pulse generation) to the RCC. When the messagelength counter decode 560 generates the CT42 pulse on conductor 562, theEOM F/F 378 is set, thus effecting the SCU reset through OR gate 30 byresetting the system control flip-flop 28.

METER TERMINAL UNIT (MTU) OPERATIONAL DESCRIPTION

The detail logic and timing for the MTU is illustrated by FIGS. 15through 22. By referring to FIGS. 15, 19, 21 and 22, it can be seen thateach of those figures is a legendary drawing showing theinterrelationships between several figures with corresponding numbers.Each of the legendary drawings comprise a designated portion of the MTU.The MTU operates in basically four modes. These modes are (1) a receivemessage mode, (2) a control mode, (3) a read and store mode and (4) atransmit mode. A great deal of the MTU logic is time shared logic andthe MTU utilizes this time shared logic in each of its operating modes.For this reason, the drawings illustrating the detailed logic of the MTUhave been segmented into figures which correspond to each of the MTUoperating modes. Further, as the ensuing description proceeds, it willbe noted that some of the time shared logic is duplicated on some of thefigures. This was done for clarity and to simplify the complexity of thedrawings. The number designations of the components on the drawingshaving like numbers are duplicated in the various drawings.

The MTU's are preferably fabricated from commercially availableintegrated circuit packages. A complete listing of the major operationalblocks as shown in the logic drawing is listed in the following Table 4.Table 4 provides a circuit name or description of the major circuitpackages, the manufacturers' names, the manufacturers' part number forthose packages and a reference to a manual or the like which providesdetailed information of the use of each of those packages.

                                      TABLE 4                                     __________________________________________________________________________    METER TERMINAL UNIT                                                           MANUFACTURERS' CIRCUIT IDENTIFICATION                                         CIRCUIT NAME                                                                  DESCRIPTION      MANUFACTURER                                                                             MANUFACTURERS' No.                                __________________________________________________________________________    MULTIPLEXERS (MPX's)                                                                            MOTOROLA.sup.1                                                                        MC14539                                                              RCA.sup.2                                                                              CD4019A                                             DEMULTIPLEXERS (DMPX's)                                                                        RCA      CD4555B                                             ALL FLIP FLOPS   RCA      CD4044A                                             RECEIVE MESSAGE  RCA      CD4015A                                             REGISTER                                                                      MTU AND SCU ADDRESS                                                                            RCA      CD4030A                                             COMPARATORS                                                                   CLOCK SYNC REG & XMIT                                                                          RCA      CD4035A                                             CLOCK REG                                                                     SYNC BITS COUNTER                                                                              RCA      CD4027A                                             CLOCK COUNTER RCA                                                                              CD4518B                                                      ALL ONE SHOTS    MOTOROLA MC14528                                             1/2 SEC DELAY COUNTER                                                                          RCA      CD4024A                                             PARITY CHECK GENERATE                                                                          NATIONAL.sup.3                                                                         MM74C174 (PLUS                                                                GATING NOT SHOWN)                                   LOAD SELECT DECODE                                                                             RCA      CD4556B FOR LOADS                                                             CD4555 FOR LIGHTS                                   PHASE LOCKED LOOP                                                                              RCA      CD4046A                                             DIVIDE BY 48 COUNTER                                                                           RCA      CD4024A                                             DIVIDE BY 5 DOWN MOTOROLA MC14522                                             COUNTER                                                                       36 BIT SHIFT REGISTERS                                                                         MOTOROLA MC14557                                             METER SELECT DECODE                                                                            RCA      CD455B                                              __________________________________________________________________________     .sup.1 All Motorola circuits can be found in the manual entitled McMOS        Integrated Circuits Data Book, copyright 1973 by Motorola Corp.               .sup.2 All RCA circuits can be found in the manual entitled COS/MOS           Integrated Circuits, copyright 1974 by RCA Corp.                              .sup.3 This circuit can be found in the manual entitled CMOS Integrated       Circuits, copyright 1975 by National Semiconductor Corp.                 

The operation of the MTU will now be described in the above sequence aspreviously mentioned. First, going through the message receive mode,then the control mode, the read and store mode and finally the transmitmode.

Prior to proceeding with the operational description of the MTU, it isconsidered advantageous at this time to review the format of the messagetransferred over the power lines from each of the SCU's to the MTU's asshown in FIG. 3. The message entering an MTU from an SCU enters in theformat as shown from the left to the right of FIG. 3. The first threebits of the message are the start code (001) bits, which are utilized bythe MTU to detect the start of a message. The following eight bits arethe SCU address which, as previously described, were reconstructed bythe SCU's address generation logic. This SCU address is utilized by theMTU as a part of its address during the receive mode operation.Following the SCU address is the previously mentioned 11 bit MTUaddress. As will be described in detail, the MTU address is decoded bythe MTU to select either one MTU, a group of eight MTU's, one section ofMTU's (e.g., one-eighth of all MTU's on a power line) or all of theMTU's on a power line or in a complete system. Following the MTU addressis the MTU function code previously noted in connection with the SCU asthe SCU/MTU function code. The MTU function code is decoded by the MTUto place that unit into a specified one of its modes of operation.Following the MTU function code is a 6-bit parity field, which ischecked by the MTU during the receive mode to see if the messagecontains valid parity. As previously described, the parity check andgenerate function of the MTU plays no part in the operation of theinvention, it merely is being shown to complete the description of thepresent disclosure.

MTU RECEIVE MODE OPERATIONAL DESCRIPTION

In the ensuing description it should be assumed that all flip-flops,registers, counters, etc. in the MTU have been reset or initialized atthe time of power application to the MTU from a source not shown.

Reference is now made to FIG. 15, which illustrates theinterrelationships between FIGS. 15A-15D. These latter figuresillustrate in detailed block diagram form the MTU logic which controlsthe message receive mode of operation. It is suggested at this time thatFIGS. 15A-15D be placed as shown by FIG. 15, since those drawingsinterconnect with each other by interfacing lines. Additionally, thetiming diagram which illustrates the operational timing of the MTUduring the message receive mode is illustrated by FIG. 16.

Reference is now made to FIG. 16 to an RF data line illustrating themessage format of data being provided to the MTU over the power lines.As previously described, a burst of energy on the power line representsa binary 0, whereas a binary 1 is represented by the absence of a burstof energy. In FIG. 16 the first three bits of RF data which enter theMTU are the sync bits 00 shown as bursts of energy and a 1, followed bythe remainder of the message. It will be noted that the messageexcluding the three sync bits, is comprised of 30 data bits shown asdotted blocks, since these data bits are indeterminate depending uponwhether they are binary 1's or binary 0's.

Reference is now made to FIG. 15A, which shows the MTU receiving the RFdata into a capacitive power line coupler low frequency attenuator 600.The power line coupler, which isolates the 60 Hz line voltage from theinput of the MTU, passes the RF data pulses to a conventionaloperational amplifier 602 via a conductor 604. The output of amplifier602 designated RF data is on a conductor 606. The RF data from amplifier602 is provided to a commutating band pass filter 608 similar to thatpreviously described in connection with the SCU. Band pass filter 608 isalso receiving an f₀ signal on a conductor 610 from an AND gate 612. Itwill be recalled that the frequency of the f₀ signal is that frequencyat which the SCU's transmit their messages over their correspondingpower lines to the MTU's. It should be mentioned that the frequency ofthe f₀ signal may be any one of several frequencies as listed in thepreviously mentioned Table 1, which allows the MTU's on various powerlines to operate at different receive frequencies.

Still referring to FIG. 15A, the f₀ signal is generated by a receiveoscillator 614 on a conductor 616 and provided to a multiplexer (MPX)618 illustrated as an electronic switch. MPX 618 receives two controlinputs, mode A and mode B, via conductors 620 and 622. The controlinputs to MPX 618 are generated by function decode logic illustrated inFIG. 19B. The generation of mode A and mode B signals will be coveredsubsequently in more detail; however, for the present let it berecognized that the mode A and mode B signals are both binary 1's atthis time. These two signals enable MPX 618 and a demultiplexer (DMPX)624 to activate their corresponding switches to connect the f₀ signalfrom the receive oscillator 614 to the input of AND gate 612 viaconductor 630. AND gate 612 is enabled at this time by a binary 1 signalon a conductor 632 from a now enabled AND gate 634 also receiving themode A and mode B signals via conductors 636 and 638, respectively.

A digression is momentarily made back to the MPX 618 of FIG. 15A, alsoreceiving an f₁ input signal from a transmit oscillator (XMIT OSC) 640via a conductor 642, and a 60 Hz pulsating signal via a conductor 644.In the present description, these two input signals have no effect onthe operation of the MTU in that those signals are utilized during theoperation of two other modes to be explained in the subsequentdescription. However, it should be noted at this time that, as thebinary configurations of the mode A and mode B signals applied to MPX618 and DMPX 624 change during subsequent operations, the switches ofthose two circuits will likewise change to the appropriate positions inaccordance with the binary configurations of the mode A and mode Bsignals.

The description now continues by reference back to the commutating bandpass filter 608, which now selects the message coming from the SCU andpasses that message via a conductor 646 to a detector circuit 648. Theoutput of detector 648 is applied to a one-shot multivibrator 650 on aconductor 652. One-shot 650 is triggered upon the detection of eachbinary 0 in the input message data stream as shown on the data line ofFIG. 16. Thus it can be seen that each time one-shot 650 is triggered, abinary 0 data bit is clocked out of that one-shot, whereas if a binary 1is detected, one-shot 650 is not fired and its output is representativeof a binary 1.

The output of one-shot 650 is simultaneously applied to three elements.one connection from one-shot 650 is the receive data (REC DATA) on aconductor 654 applied to a D or data input terminal of a message receiveregister 656 of FIG. 15B. The manner in which the receive data isclocked into register 656 will subsequently be described. The receivedata is also applied from one-shot 650 to a data input (DATA IN)terminal of a parity check generate circuit 658 of FIG. 15D via amultiplexer MPX 660 and conductors 662 and 664 (the latter conductortraverses through FIG. 15C to FIG. 15D).

Reference is now made back to FIG. 15A and to an SOM line of FIG. 16,where it is shown that the first binary 0 detected by the MTU firesone-shot 650 and applies the negative going edge of first data bit to aset input terminal of a start-of-message flip-flop SOMFF 666 on aconductor 668. As shown in FIG. 16, the SOMFF 666 sets at this timegenerating a binary 1 output signal on a conductor 670 to fire anotherone-shot designated SOM reset 672. The output of one-shot 672 is shownin FIG. 16 as a short binary 1 pulse applied as a SOM reset signal to acommon reset CR input terminal of a clock sync register 674 viaconductors 676 and 678. The purpose of the clock sync register 674 willmomentarily be described. The SOM reset signal on conductor 676 is alsoapplied to a reset terminal of the parity check generate circuit 658 ofFIG. 15D through the multiplexer 660 via conductors 680, 682 and an ORgate 684 of FIG. 15C. The parity check generate circuit 658 is now resetto receive a parity receive data on conductor 664 to check parity of theincoming message from the SCU.

Reference is now made back to FIG. 15A to the clock sync register 674and to the timing diagram of FIG. 16. It will be noted in FIG. 16 that a120 Hz pulsating signal is applied to a T input terminal of the clocksync register on a conductor 686. The 120 Hz signal is generated from amaster clock generator 688 shown in FIG. 19C. The master clock generatorreceives a 60 Hz sine wave input signal on a conductor 690 from any 60Hz source not shown (e.g., the power lines 18). It will also be notedthat the master clock generator 688 generates a 60 Hz pulsating outputsignal on a conductor 692. As will subsequently be described, the 60 Hzsignal is also utilized in the MTU to derive the appropriate timing forthat unit.

Reference is now made back to FIG. 15A and FIG. 16. The purpose of theclock sync register 674 is to synchronize the incoming data bits withclock pulses generated by that circuit. It will be recalled that the SOMreset signal caused the clock sync register 674 to reset upon thedetection of the very first binary 0 in the sync bits of the message.With the clock sync register 674 now reset, the output signal from the 0terminal of the first three flip-flops of that register on conductors694 are now binary 1's. These three binary 1 signals on conductors 694now enable an AND gate 696 to apply a binary 1 signal to a S inputterminal of the first flip-flop of register 674 via conductor 698. Asshown in FIG. 16, the first 120 Hz pulse following the SOM reset pulsecauses the first flip-flop of register 674 to be set generating apositive going basic clock signal at the output of an inverter 700 totrigger a sync bits counter 702 via conductors 704 and 706.

The clock sync register 674 is a conventional shift register which willcause a binary 1 from the first register to be clocked sequentiallythrough each of the flip-flops in that register upon the occurrence ofeach 120 Hz signal on conductor 686, thus generating a basic clockoutput signal from inverter 700 as shown in FIGS. 15A and 16. It will benoted that AND gate 696 is enabled only when the first three flip-flopsof register 674 are binary 0's. Thus, upon the occurrence of the fourth120 Hz input signal, the fourth flip-flop of register 674 will be setand the first three flip-flops will be reset, thus causing AND gate 696to be enabled to repeat the cycle as previously described. The resetsignal to the clock sync register 674 is applied from AND gate 696 whenthat AND gate is disabled by the application of a binary 1 signal to areset R input terminal of the first flip-flop of register 674 via aninverter 708 and a conductor 710.

Reference is now made to the sync bits counter 702 of FIG. 15A, which isnow counting the basic clock signals on conductor 706. When the syncbits counter 703 achieves a count of three, an AND gate 712 receivinginput signals from the counter 702 on conductors 714 is enabled togenerate a count of three, CT3, output signal on conductor 716. Thetiming for the generation of the CT3 signal is noted on the basic clockline of FIG. 16. The CT3 signal now sets a sync flip-flop 718 by theapplication of a binary 1 signal to a set S input terminal of thatflip-flop. With the sync flip-flop 718 now set, a binary 1 signal isgenerated from that flip flop's 1 output terminal on a conductor 720 tonow enable an AND gate 722, also receiving the basic clock signal at a30 Hz rate from inverter 700 on a conductor 724. Referring to FIG. 16,it can be seen that AND gate 722 now begins to generate receive clocksignals (REC clock) on a conductor 726. The purpose of the REC clock isto generate two additional signals shown in FIG. 16 as a receiver shiftregister clock (REC S/R clock) and a parity receive clock (PARITY RECCLOCK). These two signals are generated as follows.

The REC clock of conductor 726 is now applied through a multiplexer MPX728 of FIG. 15C on a conductor 730 to a trigger T input terminal of aclock counter 732. Clock counter 732 will now begin to count the RECclock pulses and provide count output signals on a plurality ofconductors 734 to a clock counter decode logic 736. Three output signalsrepresentative of binary counts in counter 732 are generated by theclock counter decode 736. It will be noted that the clock counter 732,when in a reset state, generates a binary 1 00 count output signal on aconductor 738 to apply set signals to a receive control flip-flop (RECCONT FF) 740 and a parity control flip-flop (PARITY CONT FF) 742,placing each of those flip-flops in a set state. Flip-flops 740 and 742at this time are now providing binary 1 output signals from their 1terminal on conductors 744 and 746 as one input to two AND gates 748 and750, respectively. Still referring to FIG. 15C, it will be noted thatAND gates 748 and 750 are now enabled to generate the REC S/R clocksignals on a conductor 752, and AND gate 750 is enabled to generate thePARITY REC CLOCK signals on a conductor 754. The enablement of these twoAND gates is effected by the previously mentioned input signals onconductors 744 and 746 in conjunction with the REC clock signal nowapplied on a conductor 756 from an AND gate 758. AND gate 758 isreceiving the binary 1 mode A and mode B input signals on conductors 636and 638, along with the REC clock signals on a conductor 760. The timingfor the generation of the REC S/R clock and PARITY REC CLOCK signals isshown in FIG. 16.

The PARITY REC CLOCK on conductor 754 is applied from the output of ANDgate 750 from FIG. 15C to a CL clock input terminal of the parity checkgenerate circuit 658 of FIG. 15D via the MPX 660 on a conductor 762. Itshould be noted at this time that the PARITY REC CLOCK signals now allowthe PARITY REC DATA to be clocked into the parity check generate circuit658 to allow that circuit to now begin checking message parity.Simultaneously with the clocking of the PARITY REC DATA into the paritycheck generate circuit, the REC DATA from the one-shot 650 of FIG. 15Ais clocked into the message receive register 656 under control of theREC S/R clock signal applied to that register to a CL clock inputterminal as shown in FIG. 15B.

It is significant to note at this time that the three sync, or start,bits (001) of the incoming message have been stripped off of thatmessage under control of the sync bits counter 702 in FIG. 15A. Thisremoval of the three sync pulses is illustrated by the delay in thegeneration of the REC CLOCK signal after the three sync pulses have beencounted as a result of the generation of the CT3 signal on conductor 716in FIG. 15A. This prevents the three sync bits from being clocked intothe message receive register 656.

Reference is now made back to FIG. 15C to an output conductor 780 fromthe clock counter decode 736 generating a binary 1 signal at a count of24 of the clock counter to provide a reset input signal to the REC CONTFF 740. The flip-flop 740 is reset at a count of 24 to prevent the sixparity bits of the 30-bit message from being taken into the messagereceive register 656. When the receive control flip-flop 740 resets, abinary 0 output signal on conductor 744 disables AND gate 748 to thusprevent the further application of the REC S/R clock signals onconductor 752 to the CL input terminal of the message register 656.Thus, it can be seen that the message register 656 receives only the 24data bits of the incoming message from the SCU.

The message will not continue to be clocked into the message register656 of FIG. 15B until the clock counter decode 736 of FIG. 15C decodes acount of 30 from the clock counter 732. Referring to the clock counterdecode 736, a signal T30 is generated by that decode on a conductor 764when the 30th message bit is received (see T30 of FIG. 16). The T30signal is applied to a reset R input terminal of the parity controlflip-flop 742 at this time causing the flip-flop to reset, generating abinary 0 output signal on conductor 746 to disable AND gate 750.Disabling AND gate 750 now removes the PARITY REC CLOCK signal to theparity check generate circuit 658 of FIG. 15D inhibiting the furtherclocking of the message through that circuit. Simultaneously, the T30signal on conductor 764 is applied to a set S input terminal of areceiver reset one-shot (REC RESET OS) 766 causing that one-shot togenerate a receiver reset (REC RESET) binary 1 output pulse on aconductor 768 as shown in FIGS. 15C and 16. One-shot 766 is fired on thetrailing edge of the T30 pulse as illustrated in those two figures. Thebinary 1 REC RESET signal is now applied to a reset R input terminal ofthe clock counter 732 via a multiplexer MPX 770 and conductors 772 and774. It will be noted that the MPX 770 is also receiving at this timethe mode A and mode B input signals to establish the proper switchposition for MPX 770. The application of the REC RESET signal to theclock counter 732 now causes that counter to be reset back to a binary 0state in preparation to the receipt of another message from the SCU. Itwill also be noted as shown in FIGS. 15A, 15C and 16 that the REC RESETsignal is applied to an R reset input terminal of the SOM flip-flop 666via a conductor 776, resetting that flip-flop. Additionally, the RECRESET signal is applied to the RESET input terminal of the parity checkgenerate circuit 658 via the multiplexer 660, conductors 680, 682, ORgates 684 and 778. The parity check generate circuit is now in a resetstate in preparation to the receipt of another message from the SCU.

Reference is again made back to FIG. 15C to the REC RESET output signalfrom the REC RESET OS 766. The REC RESET signal on conductor 776 is alsoapplied to a reset R input terminal of the sync bit counter 702 of FIG.15A via a conductor 782, resetting that counter in preparation toreceipt of another message from the SCU. The REC RESET signal is alsoapplied off of conductor 782 of FIG. 15A to a reset R input terminal ofthe SYNCFF 718 via conductors 784 and 786. Resetting the SYNCFF 718 nowcauses a binary 0 signal on conductor 720 to disable AND gate 722,preventing the further generation of the REC CLOCK signals.Additionally, the REC RESET signal on conductor 784 is applied as oneinput to an OR gate 788, which now passes that signal via a conductor790 to a reset R input terminal of a function strobe flip-flop FSFF 792.The FSFF 792 now resets, generating a binary 0 output signal onconductor 794 disabling the function code gating circuit 796 of FIG.15B.

At time T30 the entire message is now loaded into the message receiveregister 756 of FIG. 15B. It will be noted that the T30 signal from theclock counter decode 736 of FIG. 15C is now applied to an AND gate 798of FIG. 15D via conductors 764 and 800. AND gate 798 will be enabled atthis time to generate a function strobe enable (FUNC.STROBE EN.) signalon a conductor 802 to set the FSFF flip-flop 792, provided that allinputs to AND gate 798 are binary 1's at this time. At the leading edgeof the T30 pulse, if the parity check generate circuit 658 of FIG. 15Dhas determined that the message contains good parity, that circuit willgenerate a GOOD PARITY binary 1 output signal on a conductor 804 to seta PARITY REG FF 805. The 1 output terminal of flip-flop 805 applies abinary 1 signal on conductor 807 to AND gate 798. The purpose of thePARITY REG FF 805 is to keep AND gate 798 enabled during the transmitmode because the GOOD PARITY signal is lost during the execution of thatmode. The other inputs to AND gate 798 come from various decodefunctions from the message receive register 656 of FIG. 15B. Thedecoding of these input signals applied to AND gate 798 will now bedescribed.

Register 656 is 24 bits in length having bits or stages 3-26illustrating the format of the message as it resides in the register atT30. Bits 0, 1 and 2, not shown correspond to the three sync bitsremoved from the received message. Reference is now made to the SCUaddress field shown in FIG. 15B comprising 7 bits (3-9). As previouslydescribed in connection with FIG. 3, the SCU address was shown as eightbits; however, in the SCU the eighth bit (bit 10) is designated as amode bit having a purpose to be described. It will be recalled from theprevious description that an MTU must recognize the SCU address fromwhich it is receiving a message before that MTU can be activated. Thisis accomplished by an SCU address comparator 806 monitoring bits 3-9 ofthe SCU address from register 656 on a plurality of conductors 808 andcomparing that SCU address with a fixed SCU address provided to thecomparator 806 on a plurality of conductors 810 from an SCU addressswitches block 812. Switches 812 are set to duplicate the SCU address ofthat SCU in communication with the MTU. If the SCU address switchescompare with the SCU address from register 656, the SCU addresscomparator will generate a binary 1 output signal designated SCU ADD.COMPARE on a conductor 814. The SCU ADD. COMPARE signal on conductor 814will thus provide one of the enable input signals to AND gate 798.

Reference is now made back to FIG. 15B to that field of the messageregister 656 designated FUNC. CODE. The function code field of themessage is comprised of five bits (22-26) as previously described inconnection with FIG. 3. These five bits are decoded as bits F_(c)0-F_(c) 4 by a valid function decode (VALID FUNC. DECODE) circuit 716receiving those signals via a plurality of conductors 818 and 820 fromthe output of the message register 756. If the VALID FUNC. DECODE 816determines that the binary bit configuration of the function code is avalid MTU operation, that circuit will generate a binary 1 VALID FUNC.output signal on a conductor 822 as an additional enable input signal toAND gate 798.

Reference is now made back to FIG. 15B to the message register 656. Thatwhich remains to be described in connection with the decoding of themessage register 656 is a determination as to whether the MTU isreceiving an address designated for that MTU. As previously mentioned,each MTU in the system is capable of being individually selected,selected as a group of MTU's, a section of MTU's or selected inconjunction with all MTU's in the system or on an SCU power line.Referring to the MTU address field of register 656 of FIG. 15B, it willbe noted that that address field is comprised of bits 11-18 making upthe entire 11-bit MTU address as previously described in connection withFIG. 3. Bits 11-18 are applied via a plurality of conductors 824 to anALL MTU GATES 826 and to a comparator 828 of a pair of comparators 830.Bits 19-21 of the MTU address are applied to a comparator 832 ofcomparators 830 via a plurality of conductors 834. The comparators 830receive fixed MTU address input signals from an MTU ADD. SWITCHES block836 comprised of a set of switches 838 and 840 via a plurality ofconductors 842 and 844, respectively, connected to the comparators 828and 832. Each of the comparators 828 and 832 has its own respectiveoutput signal lines, which will become binary 1's whenever the MTUaddress from register 656 compares with the corresponding address in theMTU ADD. SWITCHES 836.

To select a single MTU, the comparators, when decoding the proper binarybit configuration of the MTU address, will generate a binary 1 outputsignal on each of two conductors 846 and 848 to enable an AND gate 850,which in turn generates a 1 MTU binary 1 output signal on a conductor852. To select 1/8, or a section, of the MTU's on a designated powerline, an AND gate 854 is enabled by a binary 1 signal on conductor 848from the comparator 832 and a binary 1 signal on conductor 856 from theALL MTU GATES 826.

The ALL MTU GATES monitor bits 11-18 to generate a binary 1 outputsignal on conductor 856 whenever the address as specified by bits 11-18specify an all MTU address.

Reference is now made to bit 10, designated MODE of register 656. Bit 10will be either a binary 1 or a binary 0 dependent upon the type of modeaddressing specified to the MTU by the message. When bit 10 is reset, abinary 0 on a conductor 858 will disable two AND gates 860 and 862. Thiswill prevent the selection of a group of eight MTU's and all MTU's.However, when the MODE bit 10 is a binary 1, AND gates 860 and 862 areconditioned to be enabled to generate a binary 1 output signal inaccordance with an address signal provided to each of those gates.Referring to AND gate 860, it will be noted that that AND gate isenabled to generate an eight MTU's binary 1 signal whenever the MODE bitis set and when the output of comparator 828 generates a binary 1 onconductor 846. Comparator 828, which monitors bits 11-18 of the MTUaddress, can thus generate a binary 1 output signal to select any numberof groups of MTU's on a designated power line limited only by the sizeof the MTU address field. When AND gate 860 is enabled, the 8 MTU'sbinary 1 address signal is generated on a conductor 864. AND gate 862 issimilarly enabled when the MODE bit is a binary 1 and bits 11-18 specifyto the ALL MTU GATES 826 an address common to all MTU's on a power lineor in the system. The combination of the binary 1 signals on conductors856 and 858 will cause AND gate 862 to generate an ALL MTU's signal on aconductor 866.

Whenever the MTU decodes an acceptable address, one of the AND gates850, 852, 854 or 860 will be enabled to apply a binary 1 signal on theircorresponding conductors to an OR gate 867 to allow that OR gate toprovide a binary 1 MTU ADD, ENABLE signal to AND gate 798 via conductor868. It can now be seen how AND gate 798 will be enabled at time T30, asshown in FIGS. 15D and 16 to set the FSFF 792 with the FUNC. STROBE EN.signal at the time the message is decoded. Assume now that all inputs toAND gate 798 are binary 1's, thus indicating the received message hasgood parity, an SCU address compare, a recognized MTU address and avalid function code. As a result, the AND gate 798 will generate abinary 1 FUNC. STROBE EN. signal on conductor 802 to set FSFF 792. Thesetting of FSFF 792 is shown in FIG. 16 on the FUNC. STROBE line,whereby that flip-flop is providing a binary 1 FUNC. STROBE signal on aconductor 794 to a function code gating 796. The FUNC. STROBE signal nowenables the function code gating circuit 796 to pass the F_(c) 0-F_(c) 4signals on conductors 818 through that gating network generating binaryoutput signals F_(c) 0'-F_(c) 4' on a plurality of conductors 870. TheF_(c) 0'-F_(c) 4' signals are provided to various decode logic in theMTU to subsequently be described. It is these signals which are decodedto determine the subsequent mode of operations that the MTU will gointo.

Reference is now made to FIG. 15D to OR gate 788 receiving the REC RESETsignal on conductor 784. As can be seen in the timing diagram of FIG.16, the REC RESET signal occurs, after the message is decoded, at thetrailing edge of the T30 pulse to reset the FSFF 792 via OR gate 788 toremove the FUNC STROBE signal from the function code gating 796 at thetime shown by the dotted lines in the FUNC STROBE pulse.

This completes the message receive mode description for the MTU. In allsubsequent descriptions, the assumption should be made that a messagehas been loaded into the message receive register 656 and that thatmessage has been decoded as a valid message with a proper address, goodparity and valid function code to activate the function code gating toallow the MTU to go into the mode specified by the F_(c) 0'-F_(c) 4'signals.

MTU Control Mode Operational Description

Reference is now made to FIGS. 17 and 18, wherein FIG. 17 shows adetailed block diagram of the load control logic for controlling aplurality of loads, or lights, external to the MTU at a designatedcustomer residence, and FIG. 18 shows the operational timing of the loadcontrol logic. In FIG. 17 the time-shared logic comprised of OR gate 788and the FSFF 792 has been duplicated for simplicity purposes to providea better understanding of the MTU control mode.

As shown in FIG. 18, the decode of the function code takes place at T30as just described for the receive mode. Let it now be assumed that theFSFF 792 is in the set state generating the FUNC STROBE signal as shownin FIG. 18. This allows the application of the F_(c) 0'-F_(c) 4' signalson conductors 870 to be simultaneously applied to a load select decodecircuit 872 via a plurality of conductors 874, a drop load decode 876via a plurality of conductors 878 and a set load decode 880 via aplurality of conductors 882. The load select decode 872 is aconventional type of binary decode logic for decoding the binaryconfigurations of the F_(c) 0'-F_(c) 4' signals. The input signals F_(c)0'-F_(c) 4', when decoded by the load select decode, cause that decodeto generate a binary 1 output signal to either set or reset a particularload or light flip-flop to that decode. It will be noted that each of aplurality of LOADFF's 886 receive set and reset input signals to their Sand R terminals on respective conductors 888 and 890. Whenever a one ofthe LOADFF's 886 is set by its corresponding binary 1 input signal onconductor 888, that flip-flop will generate a binary 1 output signal ona corresponding conductor 892 to activate a corresponding one of aplurality of switches 894. Each of the switches 894 is illustrated as aTRIAC semi-conductor type switch receiving a 24 volt AC input signalfrom a source not shown. When a binary 1 signal is applied to one of theswitches 894, the 24 volt AC signal is applied through that switch to aload connected thereto by corresponding one of conductors 896. The loadsin FIG. 17 are illustrated as having their own power source, not shown,and being external to the MTU, as these loads are generally located inthe building of the residence where the MTU is installed. Typical loadswhich can be controlled by the MTU, as previously described, are airconditioners, hot water heaters, electric clothes dryers, etc.

The load select decode 872 also provides a set and reset input signal toeach of a plurality of LIGHTFF's 898 on corresponding conductors 899.These flip-flops operate to activate their corresponding TRIAC switches895 in a fashion similar to that just described for the LOADFF's. Theswitches 895 likewise control a light in the customer's residence whichcontains its own power source. As previously described, the presentsystem is capable of turning on and off warning lights for the benefitof a customer to let him know when he is utilizing power during peakperiods so that he may reduce his load voluntarily to cut down on hispower bill. It will also be noted that each of the load flip-flops 886and 898 can be reset to disengage their corresponding load(s) or turnout their corresponding light(s) by the application of a binary 1 resetsignal to the R terminal of those flip-flops.

Referring to FIG. 18, there is shown a load or light control reset line,which illustrates the timing for the activation of either a load(s) or alight(s) flip-flop(s). A slight delay is shown between the rising edgeof the F_(c) 0'-F_(C) 4' signals compared to the load or light controlset or reset signals merely to indicate that there is a slight delay forthe loads connected to flip-flops 886 and 898 to activate or deactivatetheir corresponding loads.

Reference is now made to FIG. 17 to the set load and drop load decodecircuits 876 and 880. These two circuits receiving the F_(c) 0' andF_(c) 4' input signals will generate a binary 1 output signal on theircorresponding output conductors 900 and 902 to activate an OR gate 904whenever the message function code specifies that a load(s) is to be setor dropped out. The binary 1 signal on either of conductors 900 or 902will be passed through OR gate 904 on a conductor 906 to activate aguaranteed delay 908. The purpose of this delay 908 is to allowsufficient time for all of the loads to be either set or dropped outprior to resetting the FSFF 792. After a specified delay, delay 908 willprovide a binary 1 trigger signal to an S input terminal of a controlreset one-shot (CONT RESET OS) 910, causing that one-shot to generate acontrol reset pulse on a conductor 912 at the time as shown in FIG. 18.The control reset pulse on conductor 912 is applied to OR gate 788,causing that OR gate to now provide a binary 1 reset signal on conductor790 to the FSFF 792. Resetting the FSFF causes the function strobesignal to go to a binary 0 as shown in FIG. 18. The function strobesignal now disables the function code gating on FIG. 19B, and the MTU isin standby ready to receive another message from the SCU.

MTU Read and Store Operational Description

The MTU read and store operation is best illustrated by FIG. 19, whichis a legendary drawing showing the interrelationships between FIGS.19A-19D. In the following discussion, FIGS. 19A-19D should be positionedas shown in FIG. 19. FIGS. 20, 21A and 21B are the timing diagrams whichwill be used in the subsequent discussion of FIGS. 19A-19D. It will benoted in FIGS. 19A-19D that the time-shared logic previously describedin connection with FIGS. 15 and 19 is duplicated, wherein like numbersare assigned to like numbers of those previously discussed logicelements.

Let is now be assumed that the MTU has just completed the receivemessage mode and that a message is in the message receive register 656,which specifies in its function code that the MTU is to read and storethe meter information from one of several meters as shown in FIG. 19D.In FIG. 19D there is shown a plurality of auxiliary meters 914designated meter A1--meter AN, each having an encoder 916. Meters 916represent any number of meters at a customer residence such as gasmeters, water meters, oil meters, etc. Also shown in FIG. 19B is a mainmeter 918, having its associated encoder 920. The main meter 918customarily would be the main watt-hour meter found in a customerresidence for recording the consumption of power. As previouslymentioned, each of the encoders 916 and 920 preferred by the presentembodiment contemplates the use of an optical, serial-type read-outencoder for providing binary output signals representative of the amountof consumed commodity as documented in the aforementioned U.S. Pat. No.3,846,789. In the ensuing description, the read and store command, whichis now in the message register, will selectively specify which of themeter encoders 916 through 920 will be read in accordance with thefunction code as previously described in connection with FIG. 3.

Reference is now made to FIGS. 19B and 20. Let it now be assumed thatthe MTU has just completed the received message mode of operation asshown in FIG. 20 by the generation of the T30 pulse, which effects thedecoding of the F_(c) 0'-F_(c) 4' signals now containing the properfunction code for a read and store main meter or one of the auxiliarymeters A1-AN. Referring to FIG. 19B, the function strobe signal onconductor 794 at this time is enabling the function decode 796 to allowa function code decode logic 922 to decode the F_(c) 0'-F_(c) 4' signalsto provide the proper output signals to read and store the one of themeter encoders to be selected. Since the function code of the messagenow specifies the read and store operation, the function code circuit922 generates a binary 1 read and store (R & S) output signal on aconductor 924 to set a MODE A FF 926. The function decode 922 will alsogenerate one of two binary 1 output signals to read and store either themain meter or a selected one of the auxiliary meters in accordance withthe function code on two signal lines 928 and 930, designated R & S MAINand R & S EXT, respectively.

Reference is now made to the MODE A FF 926, which is now set. Thatflip-flop is now providing a binary 1 output signal on a conductor 932to generate a binary 1 mode A signal on a conductor 934 as shown in FIG.20. The instant that the MODE A FF 926 sets, its binary 1 output signalalso triggers a one-shot multivibrator 936 via conductors 932 and 938.One-shot 936 generates a narrow binary 1 pulse to reset a 1/2 seconddelay counter 940 and set a MODE B FF 942 via a conductor 944. With theMODE B FF 942 now set, its 1 output terminal generates a binary 1 signalon a conductor 946, which is passed through an OR gate 948 to generate abinary 1 mode B signal on a conductor 950 as shown in FIG. 20.

Still referring to FIG. 19B, it will be noted that the binary 1 outputsignal from the MODE A FF 926 is inverted to a binary 0 through aninverter 952 to generate a binary 0 mode A signal on conductor 936. In asimilar fashion, binary 1 mode B signal from OR gate 948 is inverted toa binary 0 through an inverter 954 to generate a binary 0 mode B signalon a conductor 938. At this time, the binary 0 mode A and mode B signalsare applied to the inputs of the MPX 618 and DMPX 624 of FIG. 19B,causing those two logic circuits to take on the switch positions asshown by the solid line therein. As shown in FIGS. 20 and 19B, the 60 Hzclock pulses on conductor 644 are now applied through MPX 618 and DMPX624 to trigger the input of the 1/2 second delay counter 940 via aconductor 956. Delay counter 940, as shown in FIG. 20, will continue tocount the 60 Hz pulses and, after a 1/2 second delay, will generate a1/2 SEC DELAY(DL) pulse on a conductor 958. The 1/2 SEC DL pulse is nowapplied to an AND gate 960, enabling that AND gate, due to the presenceof the binary 1 signal from the MODE A FF. AND gate 958 now applies abinary 1 signal on a conductor 962 to reset the MODE B FF 942 at thetime shown in FIG. 20.

Resetting the MODE B FF 942 applies a binary 0 signal on a conductor 946to OR gate 948, now causing the mode B signal on conductor 950 to go toa binary 0 and the mode B signal on conductor 938 to go to a binary 1.Referring now to the MPX 618 and the DMPX 624, it can be seen that themode A signal applied to those two logic circuits is still a binary 0,and the mode B signal is now a binary 1. This combination of binaryinputs now causes the MPX 618 and the DMPX 624 to switch from theposition shown by the solid switch arrow to the position now shown bythe dotted switch arrow to allow the continued application of the 60 Hzpulses on conductor 644 through those two logic units to the input ofthe 1/2 second delay counter 940.

The purpose of the 1/2 second delay can best be described by referringto FIG. 19D. In that figure, there is shown a meter select decode 964similar to the previously described load select decode receiving theF_(c) 0'-F_(c) 4' signals on conductors 870 from the function codegating 796 of FIG. 19B. The meter select decode will generate a binary 1output signal on one of a plurality of conductors 966 in accordance withthe function code to activate a corresponding one of a plurality ofTRIAC switches 968, each having its own 24 volt AC input from a powersource not shown. The activated TRIAC switch will apply 24 volt AC toits corresponding encoder 916 to start a motor in that encoder in orderto read out the information from an optical disc. Since it takes acertain amount of time for the motor in the selected encoder to come upto speed, the 1/2 second delay has been provided in the system to allowthe motor to come up to speed prior to the reading of the opticalencoder. Reference is now made back to FIG. 20 to the mode B line ofthat figure to the point showing where the MODE B FF last reset.Immediately following the resetting of the MODE B FF, there is a notebetween arrows, which says Read. It is during this period that the MTUwill now read the meter information from the selected encoder.

Reference is now made to FIGS. 21A, 21B and 19A. In FIG. 19A the 60 Hzpulses are shown being applied on conductor 644 to a phase lock loopcircuit 970, generating 2880 Hz output pulses on conductors 972 and 974.The 2880 Hz signal is applied to a trigger (T) input terminal of adivided by 48 counter 976, which divides the 2880 Hz down to regeneratea 60 Hz pulsating signal on a conductor 978 for feed-back to the phaselock loop 970. The 2880 Hz signal is also applied to an AND gate 980,also receiving a binary 1 enable input signal at this time from an ANDgate 982 via a conductor 984. It will be recalled that the mode A signalis now a binary 1 and the mode B signal is also a binary 1, thusenabling AND gate 982 to provide a binary 1 input signal to AND gate980. The 2880 Hz signals are applied on a conductor 986 to a trigger Tinput terminal of a divide by 5 down counter 988. Counter 988 alwaysstarts out in a preset count of 4, as a result of a decode zero outputsignal shown in counter 988 when that counter is reset to zero. When theMTU is first turned on, counter 988 is always zeroed out. Thus, thebinary 1 output signal from a DEC 0 terminal of counter 988 is passedthrough an OR gate 992 to a PR input terminal of counter 988 to presetthat counter to a count of four via conductors 990 and 994. Counter 988divides the 2880 Hz input signal by 5 to regenerate a read clock signalat a 576 Hz rate on a conductor 996 of FIG. 19C.

As shown in FIGS. 21A and 21B on the read clock 576 Hz line, the readclock is constantly being re-centered in the middle of each data bitbeing read from the selected meter encoder by a DATA IN (slope pulse)presetting the divide by 5 down counter 988. The DATA IN (slope pulse)is that pulse coming out of a date one-shot 998 of FIG. 19D on aconductor 1000. It will be noted in FIG. 19D that the meter encoder dataon conductor 1000 is also being read from the encoder at a 576 Hz rate.For each binary 0 bit of data read from the selected encoder, the dataone-shot 998 is triggered to generate a positive output signal to presetthe down counter 998 to a count of four via OR gate 992 as shown in FIG.19A. Thus, for each data pulse out of the encoder, the 576 Hz read clockis re-centered in the center of the bit corresponding to that data pulseto synchronize the reading of the data from the encoder with the readclock. The timing relationships between the DATA IN (slope pulse) onconductor 1000 from the data one-shot 998 and the read clock (576 Hz)pulses on conductor 996 are shown in FIGS. 21A and 21B.

As previously mentioned, the down counter 988 is preset to a count offour upon the detection by one-shot 998 of each binary 0 from theselected encoder. However, under those conditions when a binary 0 is notpresent (i.e., a binary 1 is generated), there is no output pulse fromone-shot 998. Thus, down counter 988 will not be preset. However, thisis compensated for in order to continuously generate the read clock onconductor 996 by the output from the DEC 0 terminal of counter 988 onconductor 990 to OR gate 992. If a binary 0 is not received at OR gate992, when the down counter achieves a binary count of 0, it is presetfrom the output of the DEC 0 terminal via OR gate 992. In this mannerthe 576 Hz read clock signal is continuously generated in the center ofthe DATA IN (slope pulse) as indicated in FIGS. 21A and 21B.

Reference is now made to FIGS. 21A and 21B to the data from encoder linein that timing diagram. It will be noted that digits 4 and 5 from theselected encoder precede a start code comprised of ten 1's, a 0 and a 1.This field of bits is read from the selected optical encoder and isutilized by the MTU to detect the start of the meter data indicated bythe six 6-bit fields designated ID # and digits #1 through #5.

Referring to FIG. 19D, let it now be assumed that one of the encoders916 or 920 has been commanded by the meter select decode 964 to startthat encoder's motor and thus begin reading out the meter data inserialized message form to the MTU. If the main meter 918 has beencommanded to read its encoder, the encoder optical read-out disc willbegin to generate a message on a conductor 1002 to a multiplexer MPX1004. On the other hand, if either one of the meters A1 through AN hasbeen commanded to read its encoder 916, those encoders will providetheir meter data on corresponding lines 1006 and 1008 to theircorresponding inputs of the MPX 1004. It should be noted at this timethat the two signals F_(c) 0' and F_(c) 1' are applied simultaneously tothe MPX 1004 and to and MPX 1010 from the function code gating 796 onconductors 1012 and 1014 to select the appropriate one of the meterencovers as determined by the meter select decode 964. It should benoted that the MPX 1004 has a plurality of positions which can beselected by the binary configurations of the F_(c) 0' and F_(c) 1'signals to select any one of the meter lines coming in to MPX 1004.Thus, the MPX will pass the meter data from the selected one of themeters via conductor 1016 to the S input terminal of the data one-shot998.

As previously mentioned, for each binary 0 read by the selected encoder,one-shot 998 is fired to generate a narrow data out pulse as shown online 1000. These data pulses are applied via line 1000 to the input ofan AND gate 1018 of FIG. 19A. That AND gate is now enabled to pass anyDATA IN (slope pulses) which appear at the input to that gate. This isexplained as follows:

Reference is now made back to FIG. 19B to the output of the FSFF 792generating the function strobe signal on conductor 794. With the FSFF792 set at the time shown in FIG. 20, the leading edge of the functionstrobe signal is applied via a conductor 1020 to a set S input terminalof a one-shot multivibrator 1022. One-shot 1022 generates a narrowpositive going output signal as shown in FIG. 19A, which is passedthrough an OR gate 1024 to a set S input terminal of a ten 1's FF 1026via a conductor 1028. It can now be seen that the ten 1's FF 1026 is inthe set state generating a binary 1 signal at its one-output terminal onconductor 1030 to AND gate 1018, to thus allow the DATA IN (slopepulses) to pass through that AND gate each time the date one-shot 998 ofFIG. 19D is fired.

Flip-flop 1026 is that element of the MTU which controls the detectionof the start code shown in FIGS. 21A and 21B comprised of ten 1's, a 0and a 1. Let it now be assumed that the selected meter encoder isproviding meter data via line 1000 to the input of AND gate 1018.Whenever a binary 0 is detected by data one-shot 998 of FIG. 19D, thatone-shot generates a data out pulse, which is applied to AND gate 1018enabling that AND gate. AND gate 1018 applies a binary 1 pulse to an ORgate 1032 via a conductor 1034. OR gate 1032 passes that binary 1 pulseon a conductor 1036 as a read reset signal through the now selected readinput terminal of MPX 770 via OR gate 785 and on to a reset R inputterminal of clock counter 732 via conductor 772. This will cause theclock counter 732 to reset. It should be noted at this time, as shown inFIGS. 19A and 19C, in conjunction with FIGS. 21A and 21B, that the readclock (576 Hz) signal from AND gate 1038 on conductor 996 is applied tothe trigger input terminal of the clock counter 732 via the MPX 728. Thetiming relationships between the read clock signal on conductor 996 andthe DATA IN (slope pulses) are shown in FIGS. 21A and 21B. The DATA IN(slope pulses) are shown in dotted form indicating that their presenceis indeterminate because it is not known whether they are binary 0's orbinary 1's. Also shown in FIGS. 21A and 21B, in dotted form, are theread reset pulses derived from the DATA IN (slope pulses) to reset theclock counter 732 of FIG. 19A.

Reference is now made back to AND gate 1018 of FIG. 19A. Let it now beassumed that the encoder is providing a binary 1 signal on conductor1016, which has no effect on the data one-shot 998 of FIG. 19D. Thus,the DATA IN (slope pulse) is a binary 0 disabling AND gate 1018. Theoutput of OR gate 1032 in turn goes to a binary 0, removing the binary 1read reset signal from the clock counter 732. However, the presence ofthe read clock signal on conductor 996 now causes the clock counter 732to count for each binary 1 read from the encoder. It can now be seenthat for each binary 0 read from the encoder, the clock counter 732 willbe reset, and for each binary 1 read (the absence of a pulse) the clockcounter 732 will count up by one.

Let is now be assumed that the encoder as shown in FIGS. 21A and 21B hasjust provided the binary bit configuration from digits 4 and 5 to theinput of AND gate 1018 of FIG. 19A. At the end of digit #5 as shown inFIG. 21A, the AND gate 1018 detects the first binary 1 in the start codefrom the encoder. Since the start code is comprised of ten 1's, the ANDgate 1018 will be disabled, removing the reset input to clock counter732 and allowing the read clock on conductor 996 to trigger the counter.Referring to FIG. 19A, it can be seen that when the clock counter 732achieves a binary count of 10, the clock counter decode 736 generates acount of 10 output signal on a conductor 1040. The count of 10 signal onconductor 1040 resets the ten 1's FF 1026, causing its output conductor1030 to go to a binary 0, disabling AND gate 1018.

As shown in FIG. 21A, following the ten 1's in the start code are bits 0and 1 just prior to the first bit of the ID # field. The purpose of the0 bit is to ensure that the beginning of the meter data message (ID# -digit #5) is always detected at the proper time so that the entire36-bit message is clocked into the selected one of a plurality ofstorage registers 1084 and 1058 of FIGS. 19C and 19D. The state of thebit 1 is insignificant. It could also be a bit 0 as it is not used.Referring now to FIG. 19A, there is shown an ODETFF 1041, which isutilized to detect the presence of the first binary 0 after the clockcounter 732 has counted 10 consecutive binary 1's in the encoder datamessage. The DATA IN (slope pulses) are applied to the set S inputterminal of the ODETFF 1041 from conductor 1000. Flip-flop 1041 is resetby a binary 1 signal on a conductor 1045 from the 1040 conductor outputof decode 736 when the counter 732 achieves a count of ten.

The operation of the ODETFF 1041 is as follows: Let it be assumed that ameter encoder is being read and providing binary 1 and 0 DATA IN (slopepulses) to AND gate 1018 to control the operation of the clock counter732 as just described. These DATA IN (slope pulses) are also applied tothe ODETFF 1041. It should be noted, for each binary 0 DATA IN (slopepulses) a positive going set signal is applied to flip-flop 1041. Withflip-flop 1041 set, a binary 1 signal from its 1 output terminal on aconductor 1047 keeps AND gate 1038 enabled to generate the read clockpulses. It should also be noted that a binary 1 (negative level) DATA IN(slope pulses) has no effect on flip-flop 1041. Flip-flop 1041 can onlybe set or reset on a positive going pulse.

So long as AND gate 1038 is enabled by the ODETFF 1041, the read clockpulses are applied to the T input terminal of the clock counter 732allowing it to count binary 1 DATA IN (slope pulses). Assuming now thatthe clock counter has counted ten consecutive binary 1 DATA IN (slopepulses) from the selected meter encoder. At the count of ten, thecounter decode resets the ODETFF 1041 by the generation of a binary 1signal on conductors 1040 and 1045. With flip-flop 1041 now reset, its 1output terminal goes to a binary 0 disabling AND gate 1038 via conductor1047. This stops the generation of the read clock pulses and preventsthe clock counter 732 from counting until a binary 0 (positive goingpulse) DATA IN (slope pulses) set the ODETFF 1041.

Reference is now made to FIG. 21A to the digit #5 field of the Data FromEncoder line. It is significant to note at this time that the codeutilized by the meter encoder to transmit the meter data (digits #1-#5)is a 6-bit truncated reflected binary code which does not use the allbinary 1's configuration. Thus, at least one binary 0 is guaranteed ineach digit transmitted from a selected encoder to the MTU. Utilizing theat least one binary 0, when reading a selected encoder, will guaranteethat the clock counter 732 is reset at least once for every digit readby the encoder until at least ten consecutive 1's are counted by theclock counter.

Referring to FIG. 21A to the digit #5 message field, it can now be seenthat a worst case condition for the number of binary 1's preceding thestart code would be five binary 1's in each of bits 2-6 of digit #5,because of binary 0 would have to reside in bit 1 (the all binary 1'scode is not used). Under this worst case condition, the clock counter732 of FIG. 19A will begin counting binary 1 pulses starting at the 2ndbit of digit #5 and will effect the generation of the count of tensignal on conductor 1040 ten counts later (5 counts into the start code10 1's field) to reset flip-flops 1026 and 1041. This will have noeffect, however, on the proper detection of the start of the message atthe beginning of the ID # field. This is explained in the followingparagraph.

Reference is now made to the ODETFF 1041 of FIG. 19A. Let it now beassumed that the clock counter 732 has counted ten binary 1's from theencoder under the worst case conditions as just described. As a result,flip-flop 1041 is reset, disabling AND gate 1038 stopping the readpulses on conductor 996. This stops the clock counter 732. Referring toFIG. 21A, it is noted on the Data From Encoder line that the ODETFF isreset at approximately the middle of the start code if worst case. If itis not worst case, the ODETFF will be reset at some time between thepoint shown and the bit 0 of the start code, depending on how manyconsecutive binary 1's have been counted by the clock counter 732. Afterthe ODETFF 1041 is reset, five more binary 1's of the start code areread from the encoder. As previously noted, a binary 1 DATA IN (slopepulse) has no effect on the ODETFF. Thus, it will remain reset until abinary 0 (positive pulse) is applied to its set terminal. During theperiod of these last five binary 1's of the start code, the clockcounter is inhibited from counting the read clock pulses because ANDgate 1038 is disabled. When the start code bit 0 is used from theselected encoder, the positive DATA IN (slope pulse) will set the ODETFFat the time shown in FIG. 21A. The ODETFF now re-enables AND gate 1038to re-apply the read clock pulses to the clock counter 732. The clockcounter will continue to count until it achieves a count of 48 asdetected by the clock counter decode 736 on a conductor 1042 to resetthe MTU after the complete 36-bit meter data message has been stored inthe MTU. The reset operation will subsequently be described.

Reference is now made to FIG. 19A to a clock EN flip-flop 1044. It willbe noted that flip-flop 1044 receives a binary 1 signal on a conductor738 at its set S input terminal whenever the clock counter decode 736decodes a binary count of 0 in the clock counter 732. Thus, it can beseen that the clock enable flip-flop 1044 is set each time the clockcounter is reset to generate a binary 1 R & S clock enable signal (readand store) at its 1 output terminal on a conductor 1046. The R & S clockenable signal is that signal which is utilized to enable the appropriatelogic to allow the information from the selected meter encoder to beshifted into a selected one of the previously mentioned storageregisters 1084 or 1058.

In FIGS. 21A and 21B the R & S clock enable signal is shown to be at abinary 1 at the start of the timing sequence, because the clock ENFF1044 is set upon MTU power up initialization. The R & S clock enablesignal is applied to two AND gates 1048 of FIG. 19D and 1050 of FIG. 19Cvia conductors 1046 and 1052, respectively. Reference is first made toAND gate 1048 of FIG. 19D. It will be noted that that AND gate is alsoreceiving the 576 Hz read clock signal on conductor 996 as well as the R& S clock enable signal on conductor 1046 and the R & S EXT signal onconductor 930 from the function code decode 922 of FIG. 19B. If themessage function code specifies that one of the auxiliary meter encoders916 is to be read, the R & S EXT signal 930 will be a binary 1, thusenabling AND gate 1048 to provide a READ EXT CLOCK signal on a conductor1054 to a multiplexer MPX 1056. MPX 1056 is receiving as an addresscontrol input a transmit external input signal XMIT EXT on a conductor1058 from the function code decode 922 in FIG. 19B. Since in the presentdiscussion, the function code specifies that a read and store operationis being performed, the XMIT EXT signal on conductor 1058 is a binary 0,causing the MPX 1056 to switch to the position shown in FIG. 19D. Thus,the READ EXT CLOCK signal on conductor 1054 is passed through MPX 1056to a clock CL input terminal of an Aux. 36-bit recirculating shiftregister 1058 via a conductor 1060.

If it is assumed at this time that one of the auxiliary meters A1through AN has been addressed to transfer its encoder data to the MTU,the data from the selected one of those meter encoders will be routedthrough an MPX 1010 of FIG. 19D via one of the conductors 1062 or 1064into a data DA input terminal of the register 1058 on a conductor 1066.

Referring to FIGS. 21A and 21B, it can now be seen how the timingrelationships between each of the DATA IN (slope pulses) and the readclock (576 Hz) pulses are synchronized to shift the 36-bit message froma selected one of the encoders into register 1058. It should also bepointed out at this time, as shown in FIG. 19D, that the XMIT EXT signalapplied to MPX 1056 is also applied as a binary 0 at this time to an A/Binput terminal of register 1058 on a conductor 1068. Register 1058 hasas its primary input the auxiliary meter data at its DA terminal.Register 1058 is also provided with a recirculating input fed back fromthat register's output line 1070 to a DB input terminal. When the inputsignal to the A/B terminal is a binary 0, as in the present discussion,the register 1058 serves as a straight shift register with norecirculating capabilities. However, when the input signal on conductor1068 to the A/B terminal is a binary 1, that register functions as ashift register as well as a recirculating register whereby the outputdata on conductor 1070 is recirculated back into register 1058 via theD/B terminal. The purpose of recirculating the data in register 1058will be described in connection with the transmit mode of operation.

Reference is now made to FIG. 19C to AND gate 1050 now receiving the R &S clock enable signal on conductor 1052 in conjunction with the readclock 576 Hz signal via conductors 996 and 1072. If the message functioncode specifies that the main meter encoder 920 is to be read, AND gate1050 will be enabled by the R & S MAIN signal on conductor 928 from thefunction code decode 922 of FIG. 19B. Assuming AND gate 1050 is enabled,a read main clock signal on a conductor 1074 is applied to the input ofa multiplexer MPX 1076. MPX 1076 is receiving as its control input abinary 0 XMIT MAIN signal on a conductor 1078 from the function decode922 of FIG. 19B, thus causing the MPX 1076 to be switched to theposition shown. The read main clock is thus routed through MPX 1076 intoa demultiplexer DMPX 1080 via a conductor 1082. It will be noted thatthe DMPX 1080 receives the F_(c) 0' and F_(c) 1' signals on conductors1014 and 1012, respectively. As previously explained in connection withthe two multiplexers MPX 1010 and 1004 of FIG. 19D, the binaryconfiguration of the F_(c) 0' and the F_(c) 1' signals will effect theswitch selection of the DMPX 1080 to route the read main clock into theappropriate one of a plurality of 36-bit shift registers 1084,designated 36-bit S/R A through D.

Registers 1084 operate in the same fashion as previously described forthe auxiliary 30 bit shift register 1058 of FIG. 19D. The read mainclock signal from DMPX 1080 is routed into an appropriate one of theclock CL input terminals of registers 1084 via a one of a plurality ofcorresponding conductors 1086 as selected by the DMPX 1080. Referringnow to FIGS. 19C and 19D, it will be noted that the main meter data onconductor 1002 is provided to the DA input terminal of each of theregisters 1084 via conductor 1088. It will be noted in FIG. 19C that theXMIT MAIN signal, which is now a binary 0 on conductor 1078, is appliedto each of the registers 1084 via conductor 1090 to the A/B inputterminal of each of those registers to now control their straightforward shifting as previously described in connection with register1058 of FIG. 19D.

Reference is now made back to FIG. 19A to the output of the clockcounter decode 736. Reference is also made to FIGS. 21A and 21B where itis shown that the clock counter 732 will continue to receive the readclock 576 Hz input signals from MPX 728, causing that counter to countone for each bit of the 36-bit message word from the encoder clockedinto the one of the selected 36-bit shift registers in FIGS. 19C and19D. As shown in FIG. 21B, at a count of 48 (36 message bits plus 12start code bits) by the clock counter 732, the clock counter decode 736generates a binary 1 48-count output signal on a conductor 1042, whichis applied to a set S input terminal of a R & S RESET OS 1092 (read andstore reset one-shot). The R & S RESET OS 1092 now generates a binary 1output signal R & S RESET on a conductor 1094, which is slightly delayedby one-show 1092 from the leading edge of the 48-count pulse as shown inFIGS. 19A and 21B. The R & S RESET pulse is now applied from one-shot1092 to a reset R input terminal of the CLOCK ENFF 1044 via conductor1096, resetting that flip-flop to thus cause a R & S CLOCK ENABLE signalon conductors 1046 and 1052 to go to binary 0 state to stop the shiftingof meter data into the recirculating registers 1084 and 1058.Additionally, the R & S RESET signal is applied via conductors 1098 and1099 to an OR gate 1024 of FIG. 19A. The R & S RESET signal is passedthrough OR gate 1024 via conductor 1028 to set the ten 1's FF 1026 inpreparation to receipt of another read and store command from the SCU.

Reference is now made to FIG. 19B to OR gate 788 also receiving the R &S RESET signal on conductor 1098 to now enable that OR gate to reset theFSFF 792 via conductor 790. With the FSFF now reset, its 1 outputterminal is a binary 0 on conductor 794, removing the FUNC STROBE signalfrom the function code gating, thus causing all output signals from thefunction code decode to go to a binary 0. Also in FIG. 19D, the R & SRESET signal is applied from conductor 1098 to an R reset input terminalof the MODE A FF 926 via conductor 1100. Resetting the MODE A FF causesthe Mode A signal on conductor 934 to go to a binary 0 and the mode Asignal on conductor 636 to go to a binary 1 state to place the MTU backinto the receive mode in preparation to receipt of another message fromthe SCU.

This completes the read and store mode operational description of theMTU. The MTU now contains the meter data stored in one of the selectedregisters 1084 or 1058 from a selected one of the meter encoders 916 or920 for subsequent transfer to the SCU in response to a transmit commandpresented to the MTU from the SCU. The operation of the transmit modewill now be described.

MTU Transmit Mode Operational Description

Reference is now made to FIG. 22, which is a legendary drawing showingthe inter-relationships of FIGS. 22A through 22D, the latterillustrating in detailed block diagram form the logic in the MTU forexecuting the transmit mode sequence. Like that logic previouslydescribed in connection with FIGS. 15 and 19, like logic elements inFIGS. 22A through 22D have like numbers to those corresponding numbersin FIGS. 15 and 19. To aid in the understanding of the operation of thetransmit mode sequence, it is suggested that FIGS. 22A through 22D bepositioned as shown by FIG. 22. FIG. 23 will also be referred to in thesubsequent description. FIG. 23 is a timing diagram showing theoperational sequence of the transmit mode.

Reference is now made to FIG. 22D. Let it now be assumed that the MTUhas just executed a read and store command which has caused meter datato be stored in one of the selected registers 1084 or 1058 as previouslyspecified by the function code of the read and store command. Thepurpose of the transmit command is to place the MTU in the transmit modeto transmit the data from its selected one of registers 1087 or 1058 ofFIG. 22D via the power lines to the MTU's connected SCU.

Reference is now made to FIGS. 22B and 23. Let it now be assumed thatthe MTU has just gone through the message receive sequence and the FSFF792 is set at T30 time as shown in FIG. 23 by the FUNC STROBE ENABLEsignal on conductor 802. As it will be recalled from the previousdescription, the function code and address portions of the message aredecoded at the time the function strobe on conductor 794 is provided tothe function code gating of FIG. 19B. Referring to FIGS. 19B and 23,there is shown now being generated by the function code decode 922 anXMIT mode signal on a conductor 1002 to OR gate 948 causing the mode Bsignal on conductor 950 to become a binary 1 and the mode B signal onconductor 638 to become a binary 0. FIG. 23 shows the mode B signalgoing to a binary 1 state at the time of the function strobe. It will benoted at this time that the mode A signal is a binary 0. the binarystates of the mode A and mode B signals will be utilized during thepresent description to properly switch the various multiplexers (MPX's)in the MTU to direct the clock pulses and data to the proper logicelements.

The XMIT mode signal is also provided on a conductor 1004 to variouslogic elements to be discussed. Still referring to the function codedecode 922 of FIG. 19B, the appropriate one of the XMIT MAIN or XMIT EXTlines will be a binary 1 dependent upon the contents of the messagefunction code. If the message is to be transmitted from one of the mainmeter registers 1084, the external main signal on conductor 1078 will bea binary 1. On the other hand, if the meter data is to be transmittedfrom the auxiliary 36-bit shift register 1058, the XMIT EXT line 1058will be a binary 1. The manner in which these two signals control theshifting of data out of those registers will subsequently be described.The XMIT MAIN and XMIT EXT signals are generated at the same time as theXMIT MODE signal shown in FIG. 23.

Reference is now made to FIG. 22B to the function strobe output onconductor 794, which is applied to a set S input terminal of a startcode one-shot 1104. One-shot 1104 now generates a binary 1 output pulseas shown on a conductor 1106. The signal on conductor 1106 is shown inthat figure as a START CODE S/R PRESET signal, applied to preset inputsof the flip-flops of a 3-bit start code shift register 1108. The firstflip-flop of register 1108 receives the start code shift register presetsignal on a PR1 input terminal setting that flip-flop to a binary 1. Thetwo remaining flip-flops in register 1108 each receive the preset signalon corresponding PRO terminals, presetting those two flip-flops tobinary 0's. As will subsequently be described, and as shown in FIG. 4,the three sync bits to be transmitted with the MTU message are 001.These bits now exist in the start code shift register 1108 forsubsequent transfer to the SCU.

Reference is now made to a transmit clock register 1111 of FIG. 22C.That register is now reset to all binary 0's on a conductor 1112 by abinary 1 output pulse from the 1 output terminal of a transmit resetone-shot 1114. One-shot 1114 receives the XMIT MODE signal on conductor1116 to reset the clock register 1111 at the leading edge of the XMITmode signal at the time shown in FIG. 23. Resetting register 1111 nowsynchronizes that register to begin counting the 120 Hz pulses appliedto the register on conductor 686. Register 1111 functions in the samemanner as previously described for the clock sync register 674 of FIG.15A during the receive mode sequence to shift a binary 1 through thefour stages of that register. The 0 output terminals of register 1111are connected to an AND gate 118 via a plurality of conductors 1120 tocontrol the setting and resetting of the first stage of the register viaconductors 1122, 1124 and an inverter 1126.

It will be noted that the 0 output terminals of the second and thirdstages of the transmit clock register 1111 are provided as inputs to anAND gate 1128 in conjunction with the now binary 1 XMIT MODE signal onconductor 1004. The inputs on conductors 1120 to AND gate 1128 generatea transmit (XMIT) clock signal at a 30 Hz rate on a conductor 1130. Thegeneration of the XMIT clock signal is shown in FIG. 23. AND gate 1128generates one 30 Hz XMIT clock pulse in response to each four 120 Hzinput clock pulses to register 1111 on conductor 686. Referring to FIGS.22C and 23, the first XMIT clock signal generated by AND gate 1128 isapplied via conductors 1130 and 1132 to the input of MPX 728. MPX 728 isnow addressed by the mode A and mode B signals on conductors 636 and 638to switch MPX 728 to the position shown. The binary states of the mode Aand mode B signals are shown in FIG. 23. The first transmit clock signalis now passed through MPX 728 to the trigger T input terminal of clockcounter 732, causing that counter to count to a count of one. The outputof clock counter 732 is now decoded by clock counter decode 736 togenerate a binary 1 output signal representative of the count of 01 on aconductor 1134. The 01 count signal is applied to the set S inputterminal of three flip-flops TXDATAFF 1136, PARITY CLOCKFF 1138 andSTARTCODEFF 1140, placing each of those flip-flops in a set state. The 1output terminal of each of these flip-flops is applied as an enableinput to each of three corresponding AND gates 1142, 1144 and 1146.Further, each of AND gates 1142, 1144 and 1146 is now receiving thetransmit clock signal from AND gate 1128 via conductors 1130 and 1148.As can be seen in FIG. 23, three clock signals are generated by theseAND gates designated XMIT S/R clock, PARITY XMIT CLOCK, and START CODES/R CLOCK. The start code shift register clock signal is generated byAND gate 1146 and applied to a CL clock input terminal of the start codeshift register 1108 via a conductor 1150. The parity transmit clocksignal is generated by AND gate 1144 on a conductor 1152 and applied tothe clock CLK input terminal of the parity check generate circuit 658via conductor 762 and MPX 660. It should be noted at this time that theXMIT MODE signal on conductor 1004 applied to MPX 660 is now a binary 1causing MPX 660 to switch to the position shown.

Referring now back to FIG. 22A, AND gate 1142 now provides the XMIT S/RCLOCK on a conductor 1154 to the input of MPX 1076 and MPX 1056 of FIG.22D. The MPX 1076 of FIG. 22D receives the XMIT MAIN signal on conductor1078 from the function code decode 922 of FIG. 19B. If the presentcommand specifies that the meter data is to be transferred from one ofthe main meter registers 1084, the MPX 1076 switch will be in the bottomposition as shown by the dotted line within the MPX 1076. However, ifthe XMIT MAIN signal is a binary 0, the switch will be in the upposition not allowing the XMIT S/R CLOCK to be passed through MPX 1076.Assuming that the XMIT MAIN signal is a binary 1, the XMIT S/R CLOCKwill be passed thrugh MPX 1076 into MPX 1080 via conductor 1082. MPX1080 will now have its switch position selected in accordance with thebinary states of the function code signals F_(c) 0' and F_(c) 1' fromthe output of the function code gating circuit of FIG. 19B. Dependingupon the binary configuration of the F_(c) 0' and F_(c) 1' signals, theXMIT S/R CLOCK signal will be applied to the appropriate one of theconductors 1086 to the CL terminal of the selected one of the registers1084. It should be noted at this time that the XMIT MAIN binary 1 signalon conductor 1078 is also applied via a conductor 1156 as a recirculateon XMIT signal to the A/B inputs of each of the registers 1084. Theapplication of the binary 1 signal on conductor 1156 now allows the36-bit meter data message in the selected one of the registers 1084 tobe serially shifted out to an MPX 1158 via the selected shift register'scorresponding output conductor 1160. Further, the binary 1 signalapplied to the A/B input terminals of the registers allows the selectedregister to be recirculated by having the output data on itscorresponding conductor 1160 shifted back into the register via the DBterminal. Recirculating the meter data in the selected registerpreserves that data in the event the shift register contents are neededat a later time. The data in registers 1084 and 1058 is lost only ifreplaced during a read and store operation. It should also be pointedout at this time that no meter data on conductor 1088 is shifted intothe selected register.

Still referring to FIG. 22D, it will be noted that MPX 1158 alsoreceives as address control input signals the F_(c) 0' and F_(c) 1'signals from the function code gating of FIG. 19B to select the outputof the appropriate one of the registers 1084. The output from theselected register is transferred through MPX 1158 into an MPX 1162. MPX1162 is receiving the XMIT EXT signal on conductor 1058 from thefunction code decode 922 of FIG. 19B. If the message is to betransmitted to the SCU from one of the main meter registers 1084, theXMIT EXT signal will be a binary 0, placing the MPX 1162 switch in theup position, allowing the data to be transferred from the selectedregister through MPX 1162 on to a conductor 1164.

Reference is now made to the multiplexer 1056 of FIG. 22D receiving theXMIT S/R CLOCK signal on conductor 1154. If the function code of thetransmit command specifies that the message is to be transmitted to theSCU from the auxiliary register 1058, the XMIT EXT signal on condutor1058 will select MPX 1056 to place its switch in the down position toallow the XMIT S/R CLOCK to pass through MPX 1056 into the CL terminalof register 1058. Register 1058 also receives the XMIT EXT binary 1signal on conductor 1068 at its A/B input terminal to control itscircular shifting. The message from register 1058 is transmitted out asXMIT DATA on a conductor 1070 to MPX 1162, which would now be selectedby the XMIT EXT signal to have the switch in the down position to passthe data on to conductor 1164. It can now be seen how the MTU, throughits function code and multiplexing means (MPX's), effects the selectionof the plurality of registers shown in FIG. 22D to transmit previouslystored meter data to the SCU.

Still referring to FIG. 22D, the output data from the selected one ofthe registers 1084 or 1058 on conductor 1164 is provided through MPX 660of FIG. 22B to the data in terminal of the parity check generate circuit658. The MPX switches are in the down position because of the binary 1XMIT MODE signal applied to MPX 660 on conductor 1004. The message fromthe selected one of the registers is allowed to be clocked through theparity check generate circuit 658 in response to the PARITY XMIT CLOCKon conductor 1152 now applied to the parity check generate circuit viaMPX 660 and conductor 762.

Reference is now made back to FIG. 22A to the 1 output terminal of theTXDATAFF 1136. That flip-flop, which is now set, is providing a binary 1TX DATA XMIT signal to the REC/XMIT CONT input terminal of the paritycheck generate circuit of FIG. 23B via conductors 1166, 1168 and MPX660. This binary 1 signal enables the parity check generate circuit 658to allow the PARITY XMIT DATA on conductor 1164 to be passed throughthat circuit out ot a data line 1170. The message data from the paritycheck generate circuit 658 is provided via conductor 1170 to a data Dinput terminal of the start code shift register 1108. It will be notedthat the start code shift register 1108 is now receiving the START CODES/R CLOCK pulses on conductor 1150 from now enabled AND gate 1146 ofFIG. 22A. By referring to FIG. 23, it can be seen that the XMIT S/RCLOCK, the XMIT PARITY CLOCK and the start code S/R CLOCK pulses are allgenerated in synchronism to transfer the message from the selected oneof the 36-bit shift registers in FIG. 22D out through the parity checkgenerate circuit of FIG. 22B and into the start code shift register1108.

It will be recalled at the beginning of this discussion that the startcode shift register 1108 was set to a 001 start bit configuration by thestart code S/R PRESET signal from the start code one-shot 1104. In apractical sense, the start code shift register 1108 is a 3-bit extensionof the selected one of the 36-bit shift registers 1084 or 1058. Thus,since the start code shift register and the selected one of theregisters 1084 or 1058 are synchronously shifted, the start code syncbits precede the 36-message bits as the message is shifted through thestart code shift register.

Referring now to FIG. 22B, the three sync bits are shifted out of thestart code shift register 1108, followed by the 36-message bits from theselected one of the meter data registers onto a conductor 1172 feedingthe data message to a transmitter 1174. Transmitter 1174 is alsoreceiving the RF carrier input signal f₁ via a conductor 1178 from theoutput of a DMPX 624 of FIG. 22C. The mode A and mode B signals appliedto DMPX 624 and MPX 618 are now binary 1''s, causing each of those unitsto select their switches in the position shown. As a result, the f₁carrier output signal from transmit oscillator 640 is passed through MPX618, and DMPX 624 and on to the transmitter 1174 where that carrier ismodulated by the binary 1 and 0 data message output from the start codeshift register 1108. The message is now passed through transmitter 1174on to the power line 18 via conductor 1176 and the power line coupler600 for receipt by the SCU.

Reference is now made back to FIG. 22A to the TXDATAFF 1136. Thatflip-flop receives a binary 1 reset signal via a conductor 1178 when theclock counter decode 736 detects a bit count of 36 in the clock counter732. At a count of 36 the last bit of the 36-bit message is shifted intothe first stage of the start code shift register. It is at this timethat the TXDATAFF 1136 is reset, thus providing a binary 0 signal to ANDgate 1142 preventing the further generation of XMIT S/R CLOCK signalsand simultaneously applying a binary 0 signal via conductors 1168, 1166and MPX 660 to the REC/XMIT CONT terminal of the parity check generatecircuit to inhibit the further transfer of the message to the start codeshift register.

Referring still to FIGS. 22A and 23, it can be seen that the XMIT PARITYCLOCK signal continues to be generated after the XMIT S/R CLOCK signalis terminated. The purpose of this is due to the fact that the MTU mustgenerate the proper parity for the 36 message bits previouslytransferred through the parity check generate circuit 658. Referring toFIG. 22A and 23, the PARITY CLOCKFF 1138 is reset at a clock count of 42(36 message bits plus 6 parity bits). When flip-flop 1139 resets, ANDgate 1144 is disabled, thus inhibiting the further generation of thePARITY XMIT CLOCK signals to the parity check generate circuit.

Reference is made now to FIG. 22B. In order to transmit the entiremessage (last three parity bits) out of the MTU onto the transmissionlines 18, it is necessary to generate three additional start code shiftregister clock signals to pass those three bits out of the start codeshift register 1108. The generation of these three additional clock bitsis shown in FIG. 23. The manner in which these three clock bits aregenerated is shown by the logic in FIG. 22A. Referring to the output ofthe clock counter decode 736, at a count of 45, as decoded by the clockcounter decode 736 from the clock counter 732, a binary 1 output signalresets the start code FF 1140 via a conductor 1180. When the start codeFF 1140 resets, it disables AND gate 1146 and inhibits the furthergeneration of the STATE CODE S/R CLOCK signals on conductor 1150 to thestart code shift register 1108. At a count of 45, the last message bitof meter data is shifted out of the transmitter 1174 onto the powertransmission lines 18.

Referring back to FIG. 22A, the clock counter 732 now counts one morecount to a count of 46 as detected by clock counter decode 736. Theclock counter decode now generates a binary 1 XMIT RESET signal on aconductor 1182 at the time shown in FIG. 23. The XMIT RESET signal onconductor 1182 is simultaneously applied to the MPX 770 to reset theclock counter 732 via OR gate 785 and to the reset input terminal of theparity check generate circuit 658 of FIG. 22B via MPX 660 to reset thatcircuit in preparation to receipt of another message from the SCU. TheXMIT RESET signal is also applied via conductors 1182 and 1184 to ORgate 788 to in turn reset the FSFF 792. Resetting the FSFF 792 causesthe function strobe signal on conductor 794 to go to a binary 0 state asshown in FIG. 23. The function strobe signal now going to a binary 0disables the function code gating in FIG. 19B to thus cause the transmitmode and mode B signals on conductors 1004 and 950 to each go to abinary 0 as shown in FIG. 23.

Reference is now made back to FIG. 22B to the output of OR gate 788.Upon receipt of the XMIT RESET signal by that OR gate at the time shownin FIG. 23, a binary 1 signal on a conductor 1186 is applied to theparity register flip-flop 805, resetting that flip-flop. A binary 0signal from flip-flop 805 is now applied to AND gate 798 of FIG. 15D toprevent the generation of a function strobe signal until the receipt ofanother valid message having good parity from the SCU.

The MTU is now in the standby receive mode in preparation to receipt ofanother message from the SCU as described in the receive mode operation.

While the principles of the invention have now been made clear in apreferred embodiment, there will be immediately obvious to those skilledin the art many modifications of structure, arrangement, proportions,the elements, materials and components used in the practice of theinvention and otherwise, which are particularly adapted for specificenvironments and operating requirements without departing from thoseprinciples. The appended claims are, therefore, intended to cover andembrace such modifications within the limits only of the true scope ofthe invention.

What is claimed is:
 1. In a meter terminal unit of the type for use in an automatic meter reading system, the combination comprising:(a) a source of alternating current, (b) a meter including a readable encoder electrically energizable by said alternating current for directly generating a serial stream of data signals having binary states representative of a meter measurement wherein the data signals are generated asynchronously of the alternating current; (c) clock signal generating means including synchronization means electrically responsive to said alternating current and said data signals from said encoder to provide a repetitively occurring clock signal which is synchronized with said data signals; and, (d) means for combining said clock signal and said data signals whereby said data signals are provided as identifiable measurement data synchronized by said clock signal.
 2. The meter terminal unit in accordance with claim 1 wherein said serial stream of data signals includes a specified start code of binary bits as a first portion thereof and wherein said synchronization means further includes start code recognition means responsive to said start code to enable the generation of said clock signal when said start code is recognized by said start code recognition means.
 3. The apparatus in accordance with claim 1 wherein said means for combining comprises storage means for receiving and storing the states of said data signals in response to said clock signal. 